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High sensitivity Cavity Ring Down Spectroscopy of N2O near 1.22 μm: (I) Rovibrational assignments and band-by-band analysis
Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
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High sensitivity Cavity Ring Down Spectroscopy of N2O near 1.22 μm: (I) Rovibrational assignments and band-by-band analysis E.V. Karlovets a,b,c, A. Campargue a,b,n, S. Kassi a,b, V.I. Perevalov d, S.A. Tashkun d a
Université Grenoble Alpes, LIPhy, F-38000 Grenoble, France CNRS, LIPhy, F-38000 Grenoble, France Laboratory of Quantum Mechanics of Molecules and Radiative Processes, Tomsk State University, 36 Lenina avenue, 634050 Tomsk, Russia d Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, 1 Academician Zuev Square, 634055 Tomsk, Russia b c
a r t i c l e in f o
abstract
Article history: Received 20 July 2015 Received in revised form 9 September 2015 Accepted 11 September 2015 Available online 9 October 2015
The absorption spectrum of nitrous oxide (N2O) in natural isotopic abundance has been recorded near 1.22 mm by Cavity Ring Down Spectroscopy using an External Cavity Diode Laser (ECDL) as light source. The room temperature recordings were performed at a pressure of 10.0 Torr in the 7915–8334 cm 1 spectral range (1.26–1.19 μm). The typical noise equivalent absorption of the spectra, on the order of αmin 2 10 11 cm 1, allowed for the detection of lines with intensities on the order of 5 10 29 cm/molecule. More than 3300 transitions belonging to 64 bands of five nitrous oxide isotopologues (14N216O, 14N15N16O, 15N14N16O, 14N218O and 14N217O) have been rovibrationally assigned on the basis of the predictions of the effective Hamiltonian models developed for each isotopologue. For comparison, only 13 bands were previously measured by Fourier Transform spectroscopy in the studied region. All identified bands belong to the ΔP ¼ 13 and 14 series of transitions, where P ¼ 2V1 þ V2 þ4V3 is the polyad number (Vi are vibrational quantum numbers). The line positions and intensities are provided for all assigned lines. The maximum deviations between the measured position values and those predicted by the effective Hamiltonian models are about 0.2 cm 1 for the main isotopologue but reach values larger than 1 cm 1 for the less abundant minor isotopologues. The band-by-band analysis led to the determination of the rovibrational parameters of a total of 62 bands. The typical rms value of the (νobs νfit) differences is 0.7 10 3 cm 1. Among the 62 bands, 49 are newly measured, for 13 others the rotational analysis is significantly improved and extended. A few resonance perturbations due to intra- and inter-polyad couplings are identified and discussed. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Nitrous oxide CRDS Vibration-rotational transitions Line positions Line intensities
1. Introduction
n
Corresponding author at: Université Grenoble Alpes, LIPhy, F-38000 Grenoble, France. E-mail address: [email protected] (A. Campargue). http://dx.doi.org/10.1016/j.jqsrt.2015.09.012 0022-4073/& 2015 Elsevier Ltd. All rights reserved.
In recent years, we have performed systematic investigations of the near infrared absorption spectrum of nitrous oxide by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) in the 5850–7920 cm 1 region
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
37
Fig. 3. Comparison of the CRDS spectrum of nitrous oxide in natural isotopic abundance recorded at 10 Torr with a simulation using a Voigt profile for each line. The residuals are displayed on the lower panel. Fig. 1. CRDS spectrum of nitrous oxide in natural isotopic abundance (P¼ 10 Torr). Three successive enlargements illustrate the high sensitivity and high dynamics of the recordings (noise equivalent absorption on the order of αmin 2.1 10 11 cm 1). The R branch of the 32021–10001 band 1 of 14N216O at 8010.09 cm is observed superimposed on the P branch of 1 30021-00001 band of 14N216O at 8083.95 cm .
accessible with our CRDS spectrometers by using a fiberconnected External Cavity Diode Laser (ECDL) as light source. This set up gives access to the 7915–8334 cm 1 spectral range for which only a few previous observations of N2O bands were reported [7–9]. The present report is devoted to the rovibrational assignments and band-by-band analysis. In a future contribution, the constructed experimental line list and literature data will be used for refining and improving the parameters of the global effective operators for the various nitrous oxide isotopologues. The paper is organized as follows. After a description of the experimental details (Section 2), the rovibrational assignment performed on the basis of the predictions of the effective Hamiltonian (EH) model [10–12] is presented in Section 3 together with the band by band fit. The comparison with the effective Hamiltonian predictions and the analysis of a number of intra- and inter-polyad resonance interactions are presented in Section 4.
2. Experiment Fig. 2. CRDS spectrum of nitrous oxide in natural isotopic abundance recorded at 10 Torr near 7934.4 cm 1. The displayed spectrum shows lines due to four isotopologues which are marked as: 446 (14N216O), 456 (14N15N16O), 546 (15N14N16O) and 448 (14N218O).
[1–6]. The unprecedented sensitivity of the recordings provided a considerable amount of new information. The spectral coverage was achieved thanks to a series of about ninety Distributed Feed Back (DFB) diode lasers, each of them allowing for a 30 cm 1 spectral coverage. In this work, we extend to higher frequency the spectral region
The CRDS spectrometer using a fiber-connected External Cavity Diode Laser (ECDL: Toptica DL pro, 1200 nm) is very similar to the CRDS spectrometer based on DFB diode laser used in the 5850–7920 cm 1 region. The reader is referred to Refs. [13–15] for a general description. The 1.40 m long CRDS cell is fitted by high reflectivity mirrors leading to ring down times of about 200 ms in the considered spectral interval. The CRDS cell was filled with nitrous oxide in natural isotopic abundance (Alphagaz 99.99% stated purity). The spectra were recorded at a
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E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
Table 1 Summary of the number of transitions and bands of different N2O isotopologues reported in the literature and obtained in this work by CRDS in the 7915– 8334 cm 1 region. Isotopologue
N216O N15N16O 15 14 16 N N O 14 N218O 14 N217O 14
14
a
HITRAN notation
Abundance [16,17]
446 456 546 448 447
Literature data sources are the following:
Number of bands
0.990333 3.64093 10 3 3.64093 10 3 1.98582 10 3 3.6928 10 4 Total 14
N216O [7–9],
14
N15N16O [18], and
pressure of 10.0 Torr. The temperature was observed to vary from 295.4 to 296.3 K, according to the recordings. The typical mode-hop free tuning range of this ECDL is about 0.8 cm 1. The central laser frequency was tuned by changing the grating angle together with the laser current. Consecutive and partially overlapping spectra were recorded to cover the range of interest. About 10 ring down events were averaged for each spectral data point separated by 8 10 4 cm 1. On average, one hour was needed to record a 16 cm 1 wide section of the spectrum. Overall, the spectra extend from 7915 to 8334 cm 1 (1.26–1.19 mm) but include a number of uncovered narrow intervals in particular near the high energy edge above 8300 cm 1. The sensitivity and high signal to noise are illustrated on Fig. 1. A noise equivalent absorption on the order of αmin 2.1 10 11 cm 1 is achieved. It led to the detection of a large number of lines involving many hot bands of the main isotopologue (14N216O) and bands of four minor isotopologues (15N14N16O, 14N15N16O, 14N218O and 14N217O) in natural isotopic abundance. The average density of lines is about 20 cm 1 which made the analysis particularly difficult. Lines with intensity as small as 5 10 29 cm/ molecule could be measured. As an example, Fig. 2 illustrates the congestion of the spectrum on a 1 cm 1 wide spectral interval near 7934 cm 1 where 19 lines belonging to four nitrous oxide isotopologues are observed. The wavenumber of the light emitted by the diode laser was measured by a commercial Fizeau type wavemeter (HighFinesse WSU7-IR, 5 MHz resolution, 20 MHz accuracy over 10 h) that allows laser frequency to be determined at a typical 100 Hz refresh rate. The calibration was further refined using the line positions of water vapor present as an impurity in the cell. Their values were taken from the HITRAN database [16]. We estimate to 1 10-3 cm-1 the average uncertainty on the line positions. The line centers and intensities were determined using a homemade interactive least squares multi-line fitting program. A Voigt profile was adopted as line shape. The ECDL line width ( 100 kHz Half Width at Half Maximum (HWHM)) is much smaller than the Doppler width ( 220 MHz HWHM) leading to a spectral resolution mostly Doppler limited in the adopted pressure conditions. The Gaussian HWHM was fixed to the theoretical value of the Doppler width of the 14N216O isotopologue. In general, the Lorentzian width could be fitted. In case of
Number of transitions a
This work
Literature
48 5 8 2 1 64
7 3 3 0 0 13
2640 212 331 106 33 3322
15
N14N16O [19].
weak lines or unreasonable values, it was constrained to a default value determined from nearby lines or fixed to zero. The multi-line fit provided then integrated line absorption coefficient, line center, Lorentzian width and the corresponding local baseline (assumed to be a linear function of the wavenumber). An example of line profile fitting is presented in Fig. 3. The intensity, Sv0 (cm/molecule), of a line centered at ν0, was obtained from the integrated absorption coefficient, Av0 (cm 2): Z Av0 ðTÞ ¼ αv dv ¼ Sv0 ðTÞN ð1Þ line
where ν is the wavenumber in cm 1, αν is the absorption 1 obtained from the cavity ring down coefficient in cm time, τ (in s): αν ¼ 1c 1τ τ10 , where c is the light velocity and τ0 is the ring-down time of the empty cavity and N is the molecular concentration in molecule/cm3 obtained from the measured pressure (P) and temperature (T) values: P ¼NkT (k is the Boltzmann constant).
3. Rovibrational analysis 3.1. Rovibrational assignment The assignments were carried out on the basis of the predictions of the effective Hamiltonian (EH) models of Refs. [10–12]. The corresponding EH parameters values have been fitted to the observed line positions for each isotopic species and can be found in the following references: 14N216O [10], 14N15N16O and 15N14N16O [11], 14 N218O and 14N217O [12]. The line intensities were predicted using the set of ΔP ¼14 EDM parameters of the principal isotopologue [6]. The spectrum analysis was complicated by the presence of lines due to impurities (water, carbon dioxide and methane) which were identified using the corresponding HITRAN line list [16]. The resulting global line list includes 6094 lines, 783 lines of them are due to impurities and 1989 lines are left unassigned. All unassigned lines have intensities smaller than 5 10 28 cm/molecule. The line profile of many of them is consistent with the calculated value of the Doppler broadening of N2O and we believe
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Table 2 Vibrational assignment and fractions respective to the basis states for the observed bands of 14N216O, 14N15N16O, 15N14N16O, 14N218O and 14N217O in the 7915–8334 cm 1 region. The vibrational levels are ordered in increasing order of their Gv value. Some 14N216O upper states were accessed through two bands. (P,l2,i)a
Gv
Basis states
% Fractionb
Observed band
14 14 14 14 13 14 14 14 14 13 13 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14
446 (14 0 7) (14 0 8) (14 2 14) (14 2 15) (13 1 14) (14 0 9) (14 0 10) (14 0 11) (14 2 20) (13 1 15) (13 1 16) (14 0 12) (14 2 22) (14 0 13) (15 1 7) (15 1 8) (15 1 9) (15 1 10) (15 1 11) (15 1 12) (15 1 13) (15 1 14) (16 0 10) (16 2 18) (16 0 11)
7993.346 7998.584 8001.682 8015.476 8046.349 8083.952 8145.542 8148.864 8156.703 8159.661 8266.288 8276.323 8294.117 8319.791 8547.498 8559.181 8663.158 8701.408 8704.532 8843.449 8878.283 8959.770 9108.322 9121.241 9219.055
0(10)01 /3401 140 2 /3002 0(10)21/4221/3421 2222/1422 6110/1(11)10/4510 3002/2202 0(10)01/4201 4600/1(12)00/0(14)00 0(10)21/3421/2621 6110/5310/2910 3710/4510/2910 1801/4201/5001 4221/1821 0(14)00/5400 0(11)11/3511 3112/1512 2312/3112 0(11)11/4311/2711 4710/1(13)10 5111/1911/3511/0(11)11 5510/0(15)10 5111/1911/2711 3202/1602/0802 3222/1622/0822 4002/2402/1602
34/29 32/29 19/18/16 47/36 35/19/18 44/27 26/22 27/21/17 36/29/19 28/22/17 25/24/17 22/19/17 36/26 27/27 30/30 37/32 33/32 25/20/17 25/18 24/20/17/16 25/25 29/18/16 33/23/20 39/29/19 32/20/19
(16 2 20) (16 0 14)
9244.557 9294.993
2422/3222/1622 3202/4002/2402
36/25/19 26/22/18
(16 0 15)
9398.816
5201/0(12)01/3601
c
ΔP
(16 2 27) (16 0 17) (16 2 31) (16 0 19) (17 1 10) (17 3 18) (17 1 11)
9412.966 9517.873 9542.892 9606.331 9660.968 9683.907 9783.770
52 1/36 1/0(12) 1/1(10) 1 6001/1(10)01/4401 5221/1(10)21/4421 6001 3312/0912/1712/4112 3332/1732/0932 4112/1712
27/20/19/17 21/17/16 31/21/18 25 25/24/16/16 40/27/22 32/23
(17 3 22) (17 1 14)
9820.509 9884.695
2532/1732/3332 3312/2512
36/22/20 27/22
(17 1 15) (17 3 27) (17 1 17) (18 0 9) 456 (14 0 9) (14 0 12) (14 0 14) (14 0 15) (15 1 9) 546 (14 0 7) (14 0 9) (14 0 10) (14 0 12) (14 0 14) (15 1 9) (15 1 12) (15 1 14) 447 (14 0 9) 448 (14 0 9) (14 0 14)
9958.363 9983.565 10087.195 10163.595
0(13)11/5311 5331/0(13)31/3731 6111/1(11)11 3003/2203
22/19 28/22/20 24/18 38/26
0(10)01e-0000e 1402e-0000e 0(10)21e-0000e 2222e-0000e 6110-0000 3002e-0000e 0(10)01e-0000e 4600e-0000e 0(10)21e-0000e 6110-0000 3710e-0000e 1801e-0000e 4221e-0000e 0(10)00e-0000e 0(11)11-0110 3112-0110 2312-0110 0(11)11-0110 4710-0110 5111-0110 5510f-0110f 5111-0110 3202e-0200e 3222-0220 4002e-1000e 4002e-0200e 2422-0220 3202e-1000e 3202e-0200e 5201e-1000e 5201e-0200e 5221-0220 6001e-1000e 5221f-0220f 6001e-1000e 3312-0310 3332f-0330f 4112-0310 4112-1110 2532f-0330f 3312e-0310e 3312-1110 0(13)1-0310 5331f-0330f 6111-1110 3003e-0001e
7985.547 8168.568 8284.800 8364.729 8548.772
3002/2202 4201/1801/2601 5001/3401/2601 5001/4201/3401 3112/2312
68/21 34/24/17 38/23/21 40/24/16 54/31
3002e-0000e 4201e-0000e 5001e-0000e 5001e-0000e 3112-0110
14 14 14 14 14
7918.579 7999.429 8070.796 8197.358 8292.122 8580.757 8761.411 8875.579
3002/1402 3002/2202 0(10)01/4201 1801/5001 5001 2312/3112/1512 5111/1911/3511/0(11)11 5111/1911
31/30 36/29 28/27 21/20 36 34/27/18 26/18/17/17 27/19
3002e-0000e 3002e-0000e 0(10)01e-0000e 5001e-0000e 5001e-0000e 2312-0110 5111-0110 5111f-0110f
14 14 14 14 14 14 14 14
8020.659
2202/3002/1402
36/35/22
2202-0000
14
48/41 56/20
3002e-0000e 5001e-0000e
14 14
a b c
7966.347 8132.502
2
0
2
0
30 2/22 2 5001/2601
2
25/19/18 2
Cluster labeling notation: (P¼ 2V1 þ V2 þ 4V3, l2,i): i is the order number within the cluster increasing with the energy. Squares of the expansion coefficients of the vibrational state for the dominant basis states appearing in the preceding column. V1V2ℓ2 V 3 , V2 is is given between parentheses when it is larger than 10.
40
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Fig. 4. Overview comparison between the transitions of 14N216O, 15N14N16O, 14N15N16O, 14N218O and 14N217O assigned in the CRDS spectrum of nitrous oxide in natural isotopic abundance between 7915 and 8334 cm 1 (right panels) and the corresponding spectra predicted in the frame of the effective operator approach [10–12] (left panels).
that most of the unassigned lines are due to N2O isotopologues. A summary of the observations is presented in Table 1 which gives the HITRAN notation of the various isotopologue species and the corresponding “natural” isotopic abundances as given in Ref. [17] and adopted in the HITRAN database. Five nitrous oxide isotopologues were found to contribute to the spectrum: 14N216O, 14N15N16O, 15 14 16 N N O, 14N218O and 14N217O. A total of 3322 transitions belonging to 64 bands were assigned. For comparison, only 13 bands were previously measured by Fourier Transform spectroscopy in the studied region. Note that in our region, no data are provided by the HITRAN database for N2O. All identified bands belong to the ΔP ¼ 13 and 14 series of transitions, where P¼2V1 þV2 þ4V3 is the polyad number
(Vi are vibrational quantum numbers). Among the 48 bands of 14N216O which were measured, 45 are ΔP ¼14 bands. The used rovibrational EH models are based on a polyad structure resulting from the approximate relations between the harmonic frequencies ω3 2ω1 4ω2 . As the mixing between the ðV 1 V 2 l2 V 3 Þ states may be strong, the vibrational states are preferably labeled using the (P, l2, i) triplet where the index i increases with the energy. The vibrational labeling and the dominant basis states in the vibrational decomposition of the upper states of the various bands are listed in Table 2. Note that the same ðV 1 V 2 l2 V 3 Þ state may be dominant in the eigenfunction expansion of different vibrational states.
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
41
constants have been fixed to the literature values [20,21]. The global line list provided as Supplementary material includes for each band, the fitted spectroscopic parameters of the upper state with the corresponding errors (in % and cm-1), lower state parameters and rms values of the fit together with the observed and calculated values for the line positions. 14
Fig. 5. Overview comparison of the CRDS observations of 14N216O transitions between 7915 and 8334 cm 1 with the observations available in the literature [7–9]. On the upper panel, literature observations (blue) are superimposed on the line list predicted using the effective operator approach [6,10] (gray). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Overall, 2640 transitions belonging to 48 bands were assigned to the main isotopologue. The overall list is shown in Fig. 5 where the previous observations by Fourier Transform Spectroscopy are highlighted [7–9]. The line intensities of the literature data were calculated using the set of effective dipole moment parameters of Ref. [6]. Fig. 5 illustrates that the present results considerably extend the observations in the region. Among the 48 14 N216O bands presently analyzed, only 7 were previously reported from Campargue et al. [7], Weirauch et al. [8], and Wang et al. [9] who used FTS associated with a multipass cell. Among the 48 bands analyzed, 33 are hot bands. The most excited upper level observed in this study is the (3003) state at 10163.6 cm 1 which belongs to the P¼ 18 polyad observed through the (3003)–(0001) hot band (ΔP ¼14) at 7939.8 cm 1. The constants retrieved from the fit of the line positions are listed in Table 3. The rms values of the (obs.-calc.) deviations are generally smaller than 1.0 10 3 cm 1 which is consistent with the uncertainty on the line positions. As marked in Table 4, six bands were found to be affected by perturbation, the corresponding perturbed positions were excluded from the fit. The perturbations will be analyzed in the next section. 14
Fig. 4 shows an overview comparison between the observations and the predicted spectra for the five studied nitrous oxide isotopologues. The experimental line list provided as Supplementary material includes the experimental and EH calculated positions and intensities for each line, together with corresponding rovibrational assignments. 3.2. Band by band rotational analysis In the case of unperturbed bands, the rotational analysis was performed using the standard equation for the vibration-rotation energy levels: F v ðJÞ ¼ Gv þ Bv JðJ þ 1Þ Dv J 2 ðJ þ1Þ2 þH v J 3 ðJ þ 1Þ3 ;
ð2Þ
where Gν is the vibrational term value, Bv is the rotational constant, Dv and Hv are centrifugal distortion constants. The spectroscopic parameters for an upper state were fitted directly to the observed line positions of the respective bands, and in the case of hot bands involving e and f rotational sublevels, the ee, ef, fe and ff sub bands were considered independently. The lower state rotational
N216O
N15N16O and
15
N14N16O
On the basis of the effective Hamiltonian models, a total of 212 and 331 transitions belonging to 5 and 8 bands were rovibrationally assigned for the 14N15N16O and 15N14N16O isotopologues, respectively. The previous observations in this region are limited to three bands detected for both 14 15 16 N N O [18] and 15N14N16O [19] from FTS spectra of N2O samples highly enriched in 15N. The detection of new bands of these minor isotopologues from spectra of a sample with natural isotopic abundance (3.64 10 3 for 14 15 16 N N O and 15N14N16O) illustrates the sensitivity of the present CRDS recordings. The retrieved spectroscopic constants of the 14N15N16O and 15N14N16O bands are included in Table 3. 14
N218O and
14
N217O
Two 14N218O bands and one 14N217O band were assigned in the 7915–8334 cm 1 region. The corresponding spectroscopic parameters are included in Table 3. To our knowledge, no bands of these two minor isotopologues were previously reported in the region.
42
Table 3 Spectroscopic parameters (in cm-1) for the different bands of the N2O isotopologues assigned in the CRDS spectrum between 7915 and 8334 cm 1. Lower state constants [20,21] V1V2 l2 V3a (P l2 i)b
Bv
Dv 107
(0 0 1) (1 1 1) (1 1 1) (2 2 2) (2 2 2) (2 0 1) (2 0 2) (3 3 2) (3 3 2) (3 1 1) (3 1 1) (3 1 2) (3 1 2) (4 0 1)
0.0 585.76787 585.76787 1177.74467 1177.74467 1168.13230 1284.90334 1766.91238 1766.91224 1749.06523 1749.06515 1880.26574 1880.26574 2223.75677
0.419011001 0.419177925 0.419969845 0.420125256 0.420126260 0.419920952 0.417255210 0.420667053 0.420671366 0.419583944 0.421079073 0.417464677 0.418372995 0.41555951
1.7609193 1.783245 1.793030 1.196792 1.818000 2.491945 1.726978 1.617863 1.683740 2.110353 2.177366 1.748503 1.719561 1.754675
(0 0 1) (1 1 1) (1 1 1)
0.0 575.43365 575.43365
0.418981810 0.419108916 0.419918641
1.763264 1.785826 1.794459
(0 0 1) (1 1 1) (1 1 1)
0.0 585.31212 585.31212
0.404857965 0.405037265 0.405781109
1.642938 1.656798 1.667421
(0 0 1)
0.0
0.406672154
1.663972
(0 0 1)
0.0
0.395577895
1.583456
Upper state constants V1 V2 l 2 V3 (P l2 i)
Gv
Bv
Dv 107
Hv 1012
ν0 c
Observed linesd
n/Ne
rmsf
Noteg
7993.34685(35) 7998.58422 (32) 8001.6829(50) 8015.47628(84)
0.4164357(47) 0.4094513(26) 0.416633(19) 0.4103267(24)
7.470(47) 2.165(13) -4.01(21) 1.492(16)
5.1(14) 0.26(17) -11.1(74) 2.20(30)
7993.34685(35) 7998.58422 (32) 8001.6829(50) 8015.47628(84)
1
0.4147315(14) 0.40718738(37) 0.4147647(49) 0.4194873 (56) 0.4148232(31) 0.4130802(64) 0.4106505(16) 0.4107807(26) 0.41158761(60)
2.4801(79) 1.3814(15) 16.01(30) 10.48(21) 1.0355(93) 1.703(95) 1.609(10) 0.777(11) 3.3706(70)
22/80 29/109 18/18 28/66 /4 18/18 68/68 33/80 36/55 27/27 11/12 10/10 14/18 62/62
0.88 0.93 0.90 0.97
8046.34910(42) 8083.95210(29) 8145.54283(19) 8148.86459(35) 8156.7034(24) 8159.65991(76) 8159.66173(32) 8266.2887(12) 8276.32336(12)
P49/R46h P59/R69 P39/R37 P60/R58 P9/R4 Q42 P76/R74 P58/R56 P52/R47 P50/R46 Q25 P40/R19 P46/R40 P48/R46
446 0000e 0110e 0110f 0220e 0220f 0200e 1000e 0330e 0330f 0310e 0310f 1110e 1110f 0001e 456 0000e 0110e 0110f 546 0000e 0110e 0110f 447 0000e 448 0000e
446 cold bands 0(10)01e-0000e 1402e-0000e 0(10)21e-0000e 2222e-0000e 6110e-0000e 6110f-0000e 3002e-0000e 0(10)01e-0000e 4600e-0000e 0(10)21e-0000e 6110f-0000e 6110e-0000e 3710e-0000e 1801e-0000e
(14 (14 (14 (14 (13
0 7) 0 8) 2 14) 2 15) 1 14)
(14 (14 (14 (14 (13
0 9) 0 10) 0 11) 2 20) 1 15)
(13 1 16) (14 0 12)
Hv 1012
0.016529 -0.01714 -0.01766 -2.9502 0.095 2.955393 0.146666 -0.99132 3.0154 1.2225 -0.35921 0.1075 0.21746 -0.013626
0.18666
2.451(18) 83(49) -11(21)
10.13(22)
8046.34910(42) 8083.95210(29) 8145.54283(19) 8148.86459(35) 8156.7034(24) 8159.65991(76) 8159.66173(32) 8266.2887(12) 8276.32336(12)
0.80 0.57 0.44 0.85 0.83 0.73 0.52 0.97 0.40
Previous observations
[7-9] 2
[7-9] [9] 3
[7,8]
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
Gv
Table 3 (continued) Lower state constants [20,21] V1V2 l2 V2a (P l2 i)b
Dv 107
Hv 1012
(14 2 22) (14 0 13) (14 0 14)
8294.11739(69) 8319.79197(43) 8376.5133(99)
0.4123693(18) 0.4178009(68) 0.4087782(66)
0.802(12) 12.10(14) 1.651(11)
-7.62(25)
(17 1 11)
9783.7782(19) 9783.7755(17) 9660.96801(38) 9660.97051(61) 9683.90759(29) 9219.05571(15) 10163.59545(40) 9108.32288(30) 9121.24198(24) 9121.24221(33) 8547.4981(16) 8547.51423(59) 8559.181447(96) 8559.181486(99) 9783.77001(52) 9783.77524(51) 9219.05535(22) 9244.55748(28) 9244.55778(31) 9884.69602(44) 9884.69664(44) 9294.99312(14) 9820.50949(31) 8663.15873(13) 8663.15841(14) 9398.81683(36) 8701.40887(45) 8701.40852(38) 8704.53286(38) 8704.53199(47) 9294.99391(15) 9884.69521(58) 10087.19593(70) 10087.20153(50) 9958.36342(37) 9958.36306(49) 9983.56550(46) 9398.81679(27) 9517.87355(23) 9412.96666(20) 9412.96644 (70) 8843.44953(13) 8843.44918(12)
0.4074100(43) 0.4091847(39) 0.4094924(17) 0.4117314(40) 0.4113722(18) 0.40751333(55) 0.4037158(22) 0.4103255 (29) 0.4107223(11) 0.4107332(20) 0.4149867(68) 0.4185094(54) 0.40928782(89) 0.4109353(12) 0.4074356(29) 0.4091792(26) 0.4075138(10) 0.4090108(12) 0.4090026(26) 0.4063890(17) 0.40792903(99) 0.40619595(59) 0.4097662(12) 0.40757302(37) 0.40880364(37) 0.4120047(30) 0.4138747(57) 0.4173748(72) 0.4166077(51) 0.4212481(79) 0.40618789(57) 0.4063840(46) 0.4087266(51) 0.4113240(20) 0.4106953(13) 0.4138795(19) 0.4130550(19) 0.4120056(14) 0.4094449(33) 0.4125132(11) 0.4125117 (15) 0.41075199(46) 0.41324693(56)
1.909(21) 1.965(19) 1.991(15) 1.119(26) 1.720(24) 2.3511(36) 1.392(22) 4.540(42) 0.5123(78) 1.545(29) 4.093(50) 3.92(17) 2.108(19) 2.158(31) 2.094(31) 1.910(23) 2.364(10) 1.218(12) 0.514(44) 1.325(14) 0.8276(49) 0.9108(57) 1.4593(87) 1.4801(23) 1.2914(22) 5.111(52) 13.25(16) 24.52(33) -4.17(17) -1.43(34) 0.7736(36) 1.190(67) 2.440(52) 2.374(17) 2.9613(84) 3.310(14) 1.536(15) 5.120(17) 3.02(12) -0.266(13) 2.4122(69) 2.4580(35) 2.6230(55)
10196.7322(16)
0.407339(37)
1.5(13)
(17 1 10) (17 3 18) (16 0 11) (18 0 9) (16 0 10) (16 2 18) (15 1 7) (15 1 8) (17 1 11) (16 0 11) (16 2 20) (17 1 14) (16 0 14) (17 3 22) (15 1 9) (16 0 15) (15 1 10) (15 1 11) (16 0 14) (17 1 14) (17 1 17) (17 1 15) (17 3 27) (16 0 15) (16 0 17) (16 2 27) (15 1 12) (15 1 13) (17 1 19)
11.12(82) 2.624(59) 90.1(17) 13.9(11) -8.99(81) 23.4(11) 49.8(23)
3.24(26) -3.87(34) -9.3(21)
5.68(15) 0.985(39) 1.684(36) 23.1(23) 43(13) 13(40)
23.51(57) 15.03(11) -20.57(36) 2.956(68) 1.22(14)
8294.11739(69) 8319.79197(43) 8376.5133(99)
P56/R52 P23/R11 P63
7903.51246(19) 7903.50976(17) 7911.90278(38) 7911.90536(61) 7916.99535(29) 7934.15237(15) 7939.83868(40) 7940.19058(30) 7943.49731(24) 7943.49754(33) 7961.73023(16) 7961.74636(59) 7973.413577(96) 7973.413616(99) 8034.70478(52) 8034.71009(51) 8050.92305(22) 8066.81281(28) 8066.81311(31) 8004.43028(44) 8004.43090(44) 8010.08978(14) 8053.59725(31) 8077.39086(13) 8077.39054(14) 8113.91349(36) 8115.64100(45) 8115.64065(38) 8118.76499(38) 8118.76412(47) 8126.86161(15) 8135.62998(58) 8206.93019(70) 8206.93579(50) 8209.29819(37) 8209.29791(49) 8216.65326(46) 8230.68449(27) 8232.97021(23) 8235.22199(20) 8235.22177(70) 8257.68166(13) 8257.68131(12) 8292.51684i 8316.46646(16)
R39 R40 R33 R37 R44/Q11 P18/R65 P21/R31 P23/R41 P20/R39 P25/R42/Q16 P35/R41 P46/R49 P43/R52/Q31 P40/R69/Q36 P31/R32 P34/R30 P53/R24 P50/R50 P54/R53/Q19 P37/R31 P46/R34 P53/R52 P39/R33 P66/R65/Q28 P66/R66/Q22 P31/R38 P40/R56 P47/R56 P28/R33 P21/R37 P37/R41 P29/R16 P19/R29 P33/R30 P40/R31 P33/R36 P37/R31/Q9 P47/R39 P27/R24 P53/R44/Q06 P45/R44 P64/R43/Q14 P52/R51/Q22 P14/R13 P9/R14
35/38 15/16 9/9
0.65 0.93 0.56
13/13 12/12 25/25 11/11 31/32 55/60 21/22 35/63 45/52 27/34 5/8 14/43 81/103 68/98 20/29 20/22 43/43 55/62 34/64 30/35 31/35 78/85 33/33 100/105 83/86 29/29 37/66 34/69 24/30 21/33 48/52 11/11 9/13 16/21 19/25 18/23 16/20 49/54 33/35 41/47 26/28 70/78 72/73 /5 5/6
0.74 0.82 0.79 0.91 0.67 0.63 0.77 0.87 0.89 0.71 0.86 0.59 0.36 0.30 0.94 0.98 0.68 0.82 0.74 0.98 0.82 0.57 0.75 0.60 0.59 0.82 0.99 0.73 0.66 0.58 0.57 0.69 0.81 0.61 0.71 0.89 0.72 0.78 0.43 0.71 0.96 0.57 0.46
[7-9]
4
5
[9]
[9]
6
7 0.69
43
Bv
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
4221e-0000e 0(10)01e-0000e 5001e-0000e 446 hot bands 4112e-1110e 4112f-1110f 3312e-0310e 3312f-0310f 3332f-0330f 4002e-1000e 3003e-0001e 3202e-0200e 3222e-0220e 3222f-0220f 0(11)11e-0110e 0(11)11f-0110f 3112e-0110e 3112f-0110f 4112e-0310e 4112f-0310f 4002e-0200e 2422e-0220e 2422f-0220f 3312e-1110e 3312f-1110f 3202e-1000e 2532f-0330f 2312e-0110e 2312f-0110f 5201e-1000e 0(11)11e-0110e 0(11)11f-0110f 4710e-0110e 4710f-0110f 3202e-0200e 3312e-0310e 6111e-1110e 6111f-1110f 0(13)11e-0310e 0(13)11f-0310f 5331f-0330f 5201e-0200e 6001e-1000e 5221e-0220e 5221f-0220f 5111e-0110e 5111f-0110f 5111f-0110f 6111e-1110e
Gv
10196.7333(14) 9606.33195(49) 8959.7701(34) 8959.7743(44)
0.409863(35) 0.4072714(67) 0.4089578(35) 0.4109677(40)
8.5(16) 2.64(22) 1.7264(84) 1.5586(77)
23.22(21)
(16 2 31) (14 (14 (14 (14
0 0 0 0
P14/R11 P28/R14 P55 P62 P37
8/9 20/20 15/16 7/9 /3
0.83 0.79 0.75 0.79 7
7985.54740(13) 8168.56879(28) 8284.80042(40) 8364.729(10)
0.40680698(26) 0.4117992(17) 0.4092324(49) 0.407048(15)
1.60124(93) 4.109(21) 3.15(14) 0.941(51)
7985.54740(13) 8168.56879(28) 8284.80042(40) 8364.729(10)
P49/R56 P31/R26 P30/R25 P42
74/81 27/31 27/29 5/6
0.59 0.64 0.78 0.25
(15 1 9)
8548.77283(25) 8548.77395(32)
0.40715562(83) 0.4082247(12)
1.6419(50) 1.5125(73)
7973.33918(25) 7973.34030(32)
P42/R17 P43/R24
24/29 32/36
0.53 0.88
(14 (14 (14 (14 (14
7918.57979 (29) 7999.42965(24) 8070.79646(96) 8197.35893(21) 8292.12259(22)
0.3958297 (42) 0.39385942(89) 0.4002022(55) 0.39766238(60) 0.39536948(96)
4.06(13) 1.1521(78) 5.319(77) 2.6807(32) 1.7302(97)
7918.57979 (29) 7999.42965(24) 8070.79646(96) 8197.35893(21) 8292.12259(22)
P03/R60 P56/R49 P41/R10 P34/R46 P54/R34
36/91 68/70 15/16 32/33 49/52
0.77 0.80 0.94 0.69 0.74
(15 1 14)
8580.75754(27) 8580.75759(29) 8761.41178(67) 8761.41762(63) 8875.57976(24)
0.39419944(77) 0.3954211(12) 0.3970618(37) 0.3993389(20) 0.3975009(15)
1.3017(41) 1.1031(96) 2.267(42) 2.296(12) 1.407(16)
7995.44542(27) 7995.44547(29) 8176.09966(67) 8176.10550(63) 8290.26764(24)
P47/R38 P37/R33 P25/R28 P42/R28 P31/R23
34/39 22/26 15/16 13/15 9/9
0.82 0.62 0.85 0.99 0.29
(14 0 9)
8020.65912(15)
0.3958322(12)
1.034(16)
8020.65912(15)
P28/R25
33/33
0.41
(14 0 9) (14 0 14)
7966.34701(18) 8132.50292(15)
0.3858295(66) 0.38794035(76)
0.6444(45) 2.5375(75)
7966.34701(18) 8132.50292(15)
P41/R37 P29/R33
62/62 44/44
0.69 0.48
0 0 0 0 0
9) 12) 14) 15)
8316.46756(14) 8321.42861(49) 8374.00223(34) 8374.00643(44) 8365.14736i
7) 9) 10) 12) 14)
(15 1 9) (15 1 12)
10(11) 2.29(18) 42.6(30) 5.67(25)
[18] [18] [18]
8
[19] [19]
[19]
V1V2l2V3 correspond to the maximum value of the modulo of the expansion coefficients of the eigenfunction. V2 is given between parentheses when it is larger than 10. Cluster labeling notation: (P¼ 2V1 þV2 þ 4V3, l2,i): i is the order number within the cluster increasing with the energy. c ν0 is the band center. d Observed branch with the maximum value of the total angular momentum quantum number. e n is number of transitions included in the fit; N is number of assigned transitions. f Root Mean Squares of residuals of the spectroscopic parameters fit is given in 10-3 cm-1. g Notes: 1. Intrapolyad resonance anharmonic interaction between (14 0 7)–(14 0 8) (energy levels crossing at J¼ 29). 2. Intrapolyad resonance anharmonic interaction between (14 2 14)–(14 2 15) (energy levels crossing at J¼ 45). 3. Interpolyad resonance Coriolis interaction between (14 0 11)–(13 1 15) (energy levels crossing at J¼ 38). Intrapolyad resonance anharmonic interaction between (14 0 10)–(14 0 11). 4. Intrapolyad resonance anharmonic þl-type interaction (16 0 10)–(16 2 16) (energy levels crossing at J¼26). 5. Intrapolyad resonance anharmonic interaction between (15 1 7 )–(15 1 8) (energy levels crossing at e:J ¼46, f:J ¼40). 6. Interpolyad resonance Coriolis interaction (15 1 10)–(16 0 1) (energy levels crossing at J¼ 35). Intrapolyad resonance anharmonic interaction (15 1 10)–(15 1 11). 7. A few lines. Not fitted. 8. Intrapolyad resonance anharmonic þ l-type interaction (14 0 7)–(14 2 11) (energy levels crossing at J ¼48). Intrapolyad resonance anharmonic interaction (14 0 7)–(14 0 6) (energy levels crossing at J ¼35). h The input data set of this band located near the low energy border of the investigated region was complemented with line positions previously reported in Ref. [4]. The added line positions are indicated in the Supplementary material. i Band center as provided by the global effective Hamiltonian. b
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
a
(16 0 19) (15 1 14)
44
6111f-1110f 6001e-1000e 5111e-0110e 5111f-0110f 5221f-0220f 456 cold bands 3002e-0000e 4201e-0000e 5001e-0000e 5001e-0000e 456 hot bands 3112e-0110e 3112f-0110f 546 cold bands 3002e-0000e 3002e-0000e 0(10)01e-0000e 5001e-0000e 5001e-0000e 546 hot bands 2312e-0110e 2312f-0110f 5111e-0110e 5111f-0110f 5111f-0110f 447 cold band 2202e-0000e 448 cold bands 3002e-0000e 5001e-0000e
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
4. Discussion 4.1. Comparison with the effective Hamiltonian predictions An overview comparison of the differences between the measured line positions and their predicted values [10–12] are plotted versus the wavenumber in Fig. 6. This plot illustrates the good predictive ability of the effective Hamiltonian model for 14N216O, 15N14N16O and 14N15N16O. The majority of the residuals lies between 0.03 and 0.05 cm-1. However, the line positions of the (14 0 11)– (0 0 1), (18 0 9)–(4 0 1) and (15 1 11)–(1 1 1) 14N216O bands – (4600-0000), (3003-0001) and (4710-0110) in normal mode notation- are found systematically shifted from their predicted values by values between 0.1 and 0.25 cm-1. The newly measured line positions will therefore help to significantly improve the set of the effective Hamiltonian parameters of the main isotopologue.
45
absent in the preliminary effective Hamiltonians developed for these isotopologues [12]. As a result, the deviations of the measured positions from their predicted values range between -2.0 and -1.0 cm-1 for the two bands of the 14N218O isotopologue and are about -10.5 cm-1 for the 2202e-0000e band of the 14N217O isotopologue (Fig. 6). 4.2. Rovibrational perturbations Six bands of 14N216O and the 3ν1+2ν3 band of 15N14N16O were found to be affected by perturbations which obliged us to exclude a significant number of line positions from the input data used to derive the spectroscopic constants (see Table 3). Table 4 lists for each of the perturbed band, the coupling mechanism and the J values corresponding to the energy crossing of the interacting states. When the perturbation is due to a coupling between vibrational states belonging to the same polyad, it is generally satisfactorily reproduced by the EH model but in the case of interpolyad interactions (Coriolis or anharmonic), the line positions calculated from the effective Hamiltonian or from the spectroscopic parameters (Table 3) deviate in a similar way from the measured values. The perturber and interaction mechanism of an interpolyad coupling can nevertheless be identified from the energy crossing predicted by the effective Hamiltonian model.
Fig. 6. Differences between the line positions of 14N216O, 14N15N16O, 15 14 16 N N O, 14N218O and 14N217O measured by CRDS between 7915 and 8334 cm-1 and their values predicted with the respective effective Hamiltonians. On the upper panel for the (15 1 11)–(1 1 1), (18 0 9)–(4 0 1) and (14 0 11)–(0 0 1) 14N216O bands are highlighted with triangles, rhombs and squares, respectively.
Due to a lack of the input experimental information, larger deviations are observed for the 14N218O and 14N217O isotopologues because many important parameters are
Fig. 7. Intrapolyad resonance anharmonic interaction between the (14 0 7) and the (14 0 8) upper states of 14N216O observed through the 0(10)01e-0000e and 1402e-0000e cold bands. Left hand and right hand panels show the spectrum predicted by the effective operator approach and the CRDS line lists, respectively.
46
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
Table 4 Observed perturbations of the N2O bands between 7915–8334 cm 1. Band affected
Interaction mechanism
Jcrossa
14
0(10)01-0000 1402-0000 2222-0000 4600-0000 3202-0200 3112-0110 0(11)11-0110
29 29 45 38 26 e:46 and f:40 35
15
3002-0000
Intrapolyad anharmonic (14 0 7)–(14 0 8) Intrapolyad anharmonic (14 0 8)–(14 0 7) Intrapolyad anharmonic (14 2 14)–(14 2 15) Interpolyad Coriolis (14 0 11)–(13 1 15) Intrapolyad anharmonicþ l-type (16 0 10)–(16 2 16) Intrapolyad anharmonic (15 1 7)–(15 1 8) Interpolyad Coriolis (15 1 10)–(16 0 1) þIntrapolyad anharmonic (15 1 10)–(15 1 11) Intrapolyad anharmonicþ l-type (14 0 7)–(14 2 11) þIntrapolyad anharmonic (14 0 7)–(14 0 6)
Isotopologue N216O
N14N16O
a
48 35
Value of the angular momentum quantum number at which the energy level crossing takes place.
Below we discuss in more details some of the perturbations observed for the 14N216O and 15N14N16O isotopologues. The (14 0 7) and (14 0 8) states of 14N216O are in intrapolyad anharmonic interaction. These states were observed through the 0(10)01e-0000e and 1402e-0000e cold bands at 7993.34 and 7998.58 cm-1, respectively, and are found perturbed for J values around 29. Fig. 7 shows the impact of this interaction on the rotational distribution of the 0(10)01e-0000e band and the strong intensity transfer to the 1402e-0000e band near the energy crossing. The reduced energy plot of Fig. 8 shows the energy crossing of the two interacting states.
Fig. 9. Differences between the measured values of the transition wavenumbers of the 3202e-0200e band of 14N216O at 7940.2 cm-1 ((16 0 10) upper state) and the corresponding values calculated using the EH model (upper panel) and the spectroscopic parameters of Table 3 (lower panel) versus m (where m¼ J for P-branch and m¼Jþ 1 for R-branch). The (16 0 10) upper state is perturbed by the resonance anharmonic þl-type interaction with the (16 2 16) state. Note the different ordinate scale.
Fig. 8. Reduced energy plot for the (14 0 7)–(14 0 8) interacting system of 14 N216O. Differences between the measured values of the transition wavenumbers of the bands: 0(10)01e-0000e at 7993.3 cm 1 ((14 0 7) upper state) and 1402-0000e at 7998.5 cm-1 ((14 0 8) upper state), and the corresponding values calculated using the (14 0 8) spectroscopic parameters (Table 3). For each Jupper value, the values corresponding to the R(Jupper-1) (open circle) and P(Jupper þ 1) (full circle) transitions are plotted. The (14 0 7) and (14 0 8) upper states are in intrapolyad anharmonic interaction (energy levels crossing at J ¼29).
The (16 0 10) upper state of 14N216O – (3202) in normal mode notation – is perturbed by a resonance anharmonicþ l-type interaction with the (16 2 16) state belonging to the same P¼16 polyad. Fig. 9 shows the differences between the measured values of the transition
wavenumbers of the 3202e-0200e band at 7940.2 cm 1 and the corresponding values calculated using the EH model and the spectroscopic parameters of Table 3. Near the crossing point at J ¼26, the shifts of the line positions from their unperturbed values calculated using the band parameters, reach values up to 0.1 cm 1 while they are satisfactorily predicted by the EH model. The (18 0 9) upper state of 14N216O – (3003) in normal mode notation – is affected by interpolyad resonance anharmonic interaction with (16 0 25) vibrational state. The energy level difference is about 6.5 cm 1 at J ¼0 and increases with the angular momentum quantum number J. So the perturbation is smooth and could be accounted for by the effective values of the spectroscopic constants. But
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
in the case of the global effective operators approach the resonance interaction terms should be considered explicitly. The matrix elements of the respective resonance interaction operators are listed in our paper [1]. The used polyad model of effective Hamiltonian does not take into account these terms. Because of this the line positions of the 3003-0001 band are about of -0.1 cm 1 off the experimental values. In the case of the 15N14N16O isotopologue, the 3002e0000e band ((14 0 7) upper level) is affected by two intrapolyad interactions: an anharmonicþl-type interaction with the (14 2 11) state and an anharmonic interaction with the (14 0 6) state. The interaction mechanism, the perturber state and the J value of the angular momentum quantum number corresponding to the energy crossing could be identified using the EH predictions of Ref. [11] (Table 4).
5. Conclusion Sixty four, mostly new, bands of five nitrous oxide isotopologues (14N216O, 14N15N16O, 15N14N16O, 14N218O and 14 N217O) have been rovibrationally assigned in the high sensitivity CRDS spectrum of natural nitrous oxide between 7915 and 8334 cm 1. The assignment procedure based on the predictions of the EH models was a laborious task as a result of the high density of the observed transitions and of the superimposition of the spectra of five N2O isotopologues together with impurity lines. Most of the measured transitions belong to weak hot bands of 14 N216O. The predicted line positions show an overall good agreement with the observations for the main isotopologue (maximum deviation of about 0.2 cm 1) but discrepancies increase and reach values larger than 1 cm-1 for the minor isotopologues. A few resonance perturbations were identified. They include a strong intrapolyad anharmonic interaction between the (14 0 7) and the (14 0 8) upper states of 14 N216O observed through the 0(10)01e-0000e and 1402e0000e cold bands and two interpolyad Coriolis resonance interactions which are not taken into account by the polyad model of effective Hamiltonian. The observed new data will be valuable for the refinement of the effective Hamiltonian parameters that will lead to the improvement of the quality of the prediction of the N2O line positions and intensities. The development of a non-polyad effective Hamiltonian which is in progress at IAO (Tomsk), should help us to decrease the rms deviation and assign part of the lines left unassigned in our CRDS spectra. Indeed, in all our analysis of the CRDS spectrum of nitrous oxide [1–6], a significant fraction of weak lines (about 30 %) was left unassigned. We believe that most of them are due to N2O isotopologues. Our assignment procedure rely mostly on the EH predictions, the failure to assign these lines may indicate that some important improvements are still needed in the modeling. Line intensities may provide valuable insights for the assignment of the remaining lines which are all weak or very weak. As illustrated in Fig. 7, the present status of the line intensity modeling based on the measurements of Ref. [6] is not fully satisfactory when extrapolated to the weak bands unobserved in Ref. [6], because some important dipole
47
moment parameters are unknown. For instance, some bands predicted with intensity largely above the CRDS sensitivity threshold were not detected, indicating that the corresponding predicted intensities are overestimated. The refinement of the global effective operators in particular of the ΔP¼ 13 and 14 effective dipole moment parameters, for the various nitrous oxide isotopologues will be the subject of the next contribution. In addition, the line positions of the newly measured bands of 14N218O and 14N217O will be used to refine the parameters of the effective Hamiltonians of the respective isotopologues. We hope that these improvements will help to further extend the assignments in the present spectrum.
Acknowledgments This work is jointly supported by CNRS (France) and RFBR (Russia) in the frame of the International Associated Laboratory SAMIA. This project takes place in the frame of the LabexOSUG@2020 (ANR10 LABX56).
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j. jqsrt.2015.09.012.
References [1] Liu AW, Kassi S, Malara P, Romanini D, Perevalov VI, Tashkun SA, Hu SM, Campargue A. High sensitivity CW-cavity ring down spectroscopy of N2O near 1.5 μm (I). J Mol Spectrosc 2007;244:33–47. [2] Liu AW, Kassi S, Perevalov VI, Tashkun SA, Campargue A. High sensitivity CW-cavity ring down spectroscopy of N2O near 1.50 μm (II). J Mol Spectrosc 2007;244:48–62. [3] Liu AW, Kassi S, Perevalov VI, Hu SM, Campargue A. High sensitivity CW-cavity ring down spectroscopy of N2O near 1.5 μm (III). J Mol Spectrosc 2009;254:20–7. [4] Liu AW, Kassi S, Perevalov VI, Tashkun SA, Campargue A. High sensitivity CW-cavity ring down spectroscopy of N2O near 1.28 μm. J Mol Spectrosc 2011;267:191–9. [5] Lu Y, Mondelain D, Liu AW, Perevalov VI, Kassi S, Campargue A. High sensitivity CW-cavity ring down spectroscopy of N2O between 6950 and 7653 cm 1 (1.44-1.31 μm) : I. Line positions. J Quant Spectrosc Radiat Transf 2012;113:749–62. [6] Karlovets EK, Lu Y, Mondelain D, Kassi S, Campargue, Tashkun SA, Perevalov VI. High sensitivity CW-Cavity Ring Down Spectroscopy of N2O between 6950 and 7653 cm 1 (1.44–1.31 μm): II. Line intensities. J Quant Spectrosc Radiat Transf 2013;117:81–7. [7] Campargue A, Permogorov, Bach M, Abbouti Temsamani M, Vander Auwera J, Fujii M. Overtone spectroscopy in nitrous oxide. J Chem Phys 1995;103:5931–8. [8] Weirauch G, Kachanov AA, Campargue A, Bach M, Herman M, Vander Auwera J. Refined investigation of the overtone spectrum of nitrous oxide. J Mol Spectrosc 2000;202:98–106. [9] Wang L, Perevalov VI, Tashkun SA, Gao B, Hao LY, Hu SM. Fourier transform spectroscopy of N2O weak overtone transitions in the 1–2 μm region. J Mol Spectrosc 2006;237:129–36. [10] Perevalov VI, Tashkun SA, Kochanov RV, Liu AW, Campargue A. Global modeling of the 14N216O line positions within the framework of the polyad model of effective Hamiltonian. J Quant Spectrosc Radiat Transf 2012;113:1004–12. [11] Tashkun 14 SA, Perevalov VI, Kochanov RV, Liu AW, Hu SM. Global fittings of N15N16O and 15N14N16O vibrational–rotational line positions using the effective Hamiltonian approach. J Quant Spectrosc Radiat Transf 2010;111:1089–105.
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[12] Vlasova AV, Perevalov BV, Tashkun SA, Perevalov VI. Global fittings of the line positions of the rare isotopic species of the nitrous oxide molecule. In: 13th Symposium and School on High-Resolution Molecular Spectroscopy, Leonid N. Sinitsa, Editor, Proceedings of SPIE, 2006, vol. 6580; p. 658007. [13] Macko P, Romanini D, Mikhailenko SN, Naumenko OV, Kassi S, Jenouvrier A, et al. High sensitivity CW-cavity ring down spectroscopy of water in the region of the 1.5 μm atmospheric window. J Mol Spectrosc 2004;227:90–108. [14] Morville J, Romanini D, Kachanov AA, Chenevier M. Two schemes for trace detection using cavity ringdown spectroscopy. Appl Phys 2004;D78:465–76. [15] Perevalov BV, Kassi S, Romanini D, Perevalov VI, Tashkun SA, Campargue A. CW-cavity ringdown spectroscopy of carbon dioxide isotopologues near 1.5 μm. J Mol Spectrosc 2006;238:241–55.
[16] Rothman LS, Gordon IE, Babikov YL, Barbe A, Benner DC, Bernath PF, et al. The HITRAN2012 molecular spectroscopic database. J Quant Spectrosc Radiat Transf 2013;130:4–50. [17] De Bièvre P, Holden NE, Barnes IL. Isotopic abundances and atomic weights of the elements. J Phys Chem Ref Data 1984;13:809–91. [18] Ni HY, Song KF, Perevalov VI, Tashkun SA, Liu AW, Wang L, Hu SM. Fourier-transform spectroscopy of 14N15N16O in the 38009000 cm 1 region and global modelling of its absorption spectrum. J Mol Spectrosc 2008;248:41–60. [19] Song KF, Liu AW, Ni HY, Hu SM. Fourier-transform spectroscopy of 15 14 16 N N O in the 3500-9000 cm 1 region. J Mol Spectrosc 2009;255:24–31. [20] Toth RA. Line positions and strengths of N2O between 3515 and 7800 cm 1. J Mol Spectrosc 1999;197:158–87. [21] Toth RA. Available from: 〈http://mark4sun.jpl.nasa.gov/n2o.html〉.
Contents lists available at ScienceDirect
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High sensitivity Cavity Ring Down Spectroscopy of N2O near 1.22 μm: (I) Rovibrational assignments and band-by-band analysis E.V. Karlovets a,b,c, A. Campargue a,b,n, S. Kassi a,b, V.I. Perevalov d, S.A. Tashkun d a
Université Grenoble Alpes, LIPhy, F-38000 Grenoble, France CNRS, LIPhy, F-38000 Grenoble, France Laboratory of Quantum Mechanics of Molecules and Radiative Processes, Tomsk State University, 36 Lenina avenue, 634050 Tomsk, Russia d Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, 1 Academician Zuev Square, 634055 Tomsk, Russia b c
a r t i c l e in f o
abstract
Article history: Received 20 July 2015 Received in revised form 9 September 2015 Accepted 11 September 2015 Available online 9 October 2015
The absorption spectrum of nitrous oxide (N2O) in natural isotopic abundance has been recorded near 1.22 mm by Cavity Ring Down Spectroscopy using an External Cavity Diode Laser (ECDL) as light source. The room temperature recordings were performed at a pressure of 10.0 Torr in the 7915–8334 cm 1 spectral range (1.26–1.19 μm). The typical noise equivalent absorption of the spectra, on the order of αmin 2 10 11 cm 1, allowed for the detection of lines with intensities on the order of 5 10 29 cm/molecule. More than 3300 transitions belonging to 64 bands of five nitrous oxide isotopologues (14N216O, 14N15N16O, 15N14N16O, 14N218O and 14N217O) have been rovibrationally assigned on the basis of the predictions of the effective Hamiltonian models developed for each isotopologue. For comparison, only 13 bands were previously measured by Fourier Transform spectroscopy in the studied region. All identified bands belong to the ΔP ¼ 13 and 14 series of transitions, where P ¼ 2V1 þ V2 þ4V3 is the polyad number (Vi are vibrational quantum numbers). The line positions and intensities are provided for all assigned lines. The maximum deviations between the measured position values and those predicted by the effective Hamiltonian models are about 0.2 cm 1 for the main isotopologue but reach values larger than 1 cm 1 for the less abundant minor isotopologues. The band-by-band analysis led to the determination of the rovibrational parameters of a total of 62 bands. The typical rms value of the (νobs νfit) differences is 0.7 10 3 cm 1. Among the 62 bands, 49 are newly measured, for 13 others the rotational analysis is significantly improved and extended. A few resonance perturbations due to intra- and inter-polyad couplings are identified and discussed. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Nitrous oxide CRDS Vibration-rotational transitions Line positions Line intensities
1. Introduction
n
Corresponding author at: Université Grenoble Alpes, LIPhy, F-38000 Grenoble, France. E-mail address: [email protected] (A. Campargue). http://dx.doi.org/10.1016/j.jqsrt.2015.09.012 0022-4073/& 2015 Elsevier Ltd. All rights reserved.
In recent years, we have performed systematic investigations of the near infrared absorption spectrum of nitrous oxide by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) in the 5850–7920 cm 1 region
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
37
Fig. 3. Comparison of the CRDS spectrum of nitrous oxide in natural isotopic abundance recorded at 10 Torr with a simulation using a Voigt profile for each line. The residuals are displayed on the lower panel. Fig. 1. CRDS spectrum of nitrous oxide in natural isotopic abundance (P¼ 10 Torr). Three successive enlargements illustrate the high sensitivity and high dynamics of the recordings (noise equivalent absorption on the order of αmin 2.1 10 11 cm 1). The R branch of the 32021–10001 band 1 of 14N216O at 8010.09 cm is observed superimposed on the P branch of 1 30021-00001 band of 14N216O at 8083.95 cm .
accessible with our CRDS spectrometers by using a fiberconnected External Cavity Diode Laser (ECDL) as light source. This set up gives access to the 7915–8334 cm 1 spectral range for which only a few previous observations of N2O bands were reported [7–9]. The present report is devoted to the rovibrational assignments and band-by-band analysis. In a future contribution, the constructed experimental line list and literature data will be used for refining and improving the parameters of the global effective operators for the various nitrous oxide isotopologues. The paper is organized as follows. After a description of the experimental details (Section 2), the rovibrational assignment performed on the basis of the predictions of the effective Hamiltonian (EH) model [10–12] is presented in Section 3 together with the band by band fit. The comparison with the effective Hamiltonian predictions and the analysis of a number of intra- and inter-polyad resonance interactions are presented in Section 4.
2. Experiment Fig. 2. CRDS spectrum of nitrous oxide in natural isotopic abundance recorded at 10 Torr near 7934.4 cm 1. The displayed spectrum shows lines due to four isotopologues which are marked as: 446 (14N216O), 456 (14N15N16O), 546 (15N14N16O) and 448 (14N218O).
[1–6]. The unprecedented sensitivity of the recordings provided a considerable amount of new information. The spectral coverage was achieved thanks to a series of about ninety Distributed Feed Back (DFB) diode lasers, each of them allowing for a 30 cm 1 spectral coverage. In this work, we extend to higher frequency the spectral region
The CRDS spectrometer using a fiber-connected External Cavity Diode Laser (ECDL: Toptica DL pro, 1200 nm) is very similar to the CRDS spectrometer based on DFB diode laser used in the 5850–7920 cm 1 region. The reader is referred to Refs. [13–15] for a general description. The 1.40 m long CRDS cell is fitted by high reflectivity mirrors leading to ring down times of about 200 ms in the considered spectral interval. The CRDS cell was filled with nitrous oxide in natural isotopic abundance (Alphagaz 99.99% stated purity). The spectra were recorded at a
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Table 1 Summary of the number of transitions and bands of different N2O isotopologues reported in the literature and obtained in this work by CRDS in the 7915– 8334 cm 1 region. Isotopologue
N216O N15N16O 15 14 16 N N O 14 N218O 14 N217O 14
14
a
HITRAN notation
Abundance [16,17]
446 456 546 448 447
Literature data sources are the following:
Number of bands
0.990333 3.64093 10 3 3.64093 10 3 1.98582 10 3 3.6928 10 4 Total 14
N216O [7–9],
14
N15N16O [18], and
pressure of 10.0 Torr. The temperature was observed to vary from 295.4 to 296.3 K, according to the recordings. The typical mode-hop free tuning range of this ECDL is about 0.8 cm 1. The central laser frequency was tuned by changing the grating angle together with the laser current. Consecutive and partially overlapping spectra were recorded to cover the range of interest. About 10 ring down events were averaged for each spectral data point separated by 8 10 4 cm 1. On average, one hour was needed to record a 16 cm 1 wide section of the spectrum. Overall, the spectra extend from 7915 to 8334 cm 1 (1.26–1.19 mm) but include a number of uncovered narrow intervals in particular near the high energy edge above 8300 cm 1. The sensitivity and high signal to noise are illustrated on Fig. 1. A noise equivalent absorption on the order of αmin 2.1 10 11 cm 1 is achieved. It led to the detection of a large number of lines involving many hot bands of the main isotopologue (14N216O) and bands of four minor isotopologues (15N14N16O, 14N15N16O, 14N218O and 14N217O) in natural isotopic abundance. The average density of lines is about 20 cm 1 which made the analysis particularly difficult. Lines with intensity as small as 5 10 29 cm/ molecule could be measured. As an example, Fig. 2 illustrates the congestion of the spectrum on a 1 cm 1 wide spectral interval near 7934 cm 1 where 19 lines belonging to four nitrous oxide isotopologues are observed. The wavenumber of the light emitted by the diode laser was measured by a commercial Fizeau type wavemeter (HighFinesse WSU7-IR, 5 MHz resolution, 20 MHz accuracy over 10 h) that allows laser frequency to be determined at a typical 100 Hz refresh rate. The calibration was further refined using the line positions of water vapor present as an impurity in the cell. Their values were taken from the HITRAN database [16]. We estimate to 1 10-3 cm-1 the average uncertainty on the line positions. The line centers and intensities were determined using a homemade interactive least squares multi-line fitting program. A Voigt profile was adopted as line shape. The ECDL line width ( 100 kHz Half Width at Half Maximum (HWHM)) is much smaller than the Doppler width ( 220 MHz HWHM) leading to a spectral resolution mostly Doppler limited in the adopted pressure conditions. The Gaussian HWHM was fixed to the theoretical value of the Doppler width of the 14N216O isotopologue. In general, the Lorentzian width could be fitted. In case of
Number of transitions a
This work
Literature
48 5 8 2 1 64
7 3 3 0 0 13
2640 212 331 106 33 3322
15
N14N16O [19].
weak lines or unreasonable values, it was constrained to a default value determined from nearby lines or fixed to zero. The multi-line fit provided then integrated line absorption coefficient, line center, Lorentzian width and the corresponding local baseline (assumed to be a linear function of the wavenumber). An example of line profile fitting is presented in Fig. 3. The intensity, Sv0 (cm/molecule), of a line centered at ν0, was obtained from the integrated absorption coefficient, Av0 (cm 2): Z Av0 ðTÞ ¼ αv dv ¼ Sv0 ðTÞN ð1Þ line
where ν is the wavenumber in cm 1, αν is the absorption 1 obtained from the cavity ring down coefficient in cm time, τ (in s): αν ¼ 1c 1τ τ10 , where c is the light velocity and τ0 is the ring-down time of the empty cavity and N is the molecular concentration in molecule/cm3 obtained from the measured pressure (P) and temperature (T) values: P ¼NkT (k is the Boltzmann constant).
3. Rovibrational analysis 3.1. Rovibrational assignment The assignments were carried out on the basis of the predictions of the effective Hamiltonian (EH) models of Refs. [10–12]. The corresponding EH parameters values have been fitted to the observed line positions for each isotopic species and can be found in the following references: 14N216O [10], 14N15N16O and 15N14N16O [11], 14 N218O and 14N217O [12]. The line intensities were predicted using the set of ΔP ¼14 EDM parameters of the principal isotopologue [6]. The spectrum analysis was complicated by the presence of lines due to impurities (water, carbon dioxide and methane) which were identified using the corresponding HITRAN line list [16]. The resulting global line list includes 6094 lines, 783 lines of them are due to impurities and 1989 lines are left unassigned. All unassigned lines have intensities smaller than 5 10 28 cm/molecule. The line profile of many of them is consistent with the calculated value of the Doppler broadening of N2O and we believe
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Table 2 Vibrational assignment and fractions respective to the basis states for the observed bands of 14N216O, 14N15N16O, 15N14N16O, 14N218O and 14N217O in the 7915–8334 cm 1 region. The vibrational levels are ordered in increasing order of their Gv value. Some 14N216O upper states were accessed through two bands. (P,l2,i)a
Gv
Basis states
% Fractionb
Observed band
14 14 14 14 13 14 14 14 14 13 13 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14 14
446 (14 0 7) (14 0 8) (14 2 14) (14 2 15) (13 1 14) (14 0 9) (14 0 10) (14 0 11) (14 2 20) (13 1 15) (13 1 16) (14 0 12) (14 2 22) (14 0 13) (15 1 7) (15 1 8) (15 1 9) (15 1 10) (15 1 11) (15 1 12) (15 1 13) (15 1 14) (16 0 10) (16 2 18) (16 0 11)
7993.346 7998.584 8001.682 8015.476 8046.349 8083.952 8145.542 8148.864 8156.703 8159.661 8266.288 8276.323 8294.117 8319.791 8547.498 8559.181 8663.158 8701.408 8704.532 8843.449 8878.283 8959.770 9108.322 9121.241 9219.055
0(10)01 /3401 140 2 /3002 0(10)21/4221/3421 2222/1422 6110/1(11)10/4510 3002/2202 0(10)01/4201 4600/1(12)00/0(14)00 0(10)21/3421/2621 6110/5310/2910 3710/4510/2910 1801/4201/5001 4221/1821 0(14)00/5400 0(11)11/3511 3112/1512 2312/3112 0(11)11/4311/2711 4710/1(13)10 5111/1911/3511/0(11)11 5510/0(15)10 5111/1911/2711 3202/1602/0802 3222/1622/0822 4002/2402/1602
34/29 32/29 19/18/16 47/36 35/19/18 44/27 26/22 27/21/17 36/29/19 28/22/17 25/24/17 22/19/17 36/26 27/27 30/30 37/32 33/32 25/20/17 25/18 24/20/17/16 25/25 29/18/16 33/23/20 39/29/19 32/20/19
(16 2 20) (16 0 14)
9244.557 9294.993
2422/3222/1622 3202/4002/2402
36/25/19 26/22/18
(16 0 15)
9398.816
5201/0(12)01/3601
c
ΔP
(16 2 27) (16 0 17) (16 2 31) (16 0 19) (17 1 10) (17 3 18) (17 1 11)
9412.966 9517.873 9542.892 9606.331 9660.968 9683.907 9783.770
52 1/36 1/0(12) 1/1(10) 1 6001/1(10)01/4401 5221/1(10)21/4421 6001 3312/0912/1712/4112 3332/1732/0932 4112/1712
27/20/19/17 21/17/16 31/21/18 25 25/24/16/16 40/27/22 32/23
(17 3 22) (17 1 14)
9820.509 9884.695
2532/1732/3332 3312/2512
36/22/20 27/22
(17 1 15) (17 3 27) (17 1 17) (18 0 9) 456 (14 0 9) (14 0 12) (14 0 14) (14 0 15) (15 1 9) 546 (14 0 7) (14 0 9) (14 0 10) (14 0 12) (14 0 14) (15 1 9) (15 1 12) (15 1 14) 447 (14 0 9) 448 (14 0 9) (14 0 14)
9958.363 9983.565 10087.195 10163.595
0(13)11/5311 5331/0(13)31/3731 6111/1(11)11 3003/2203
22/19 28/22/20 24/18 38/26
0(10)01e-0000e 1402e-0000e 0(10)21e-0000e 2222e-0000e 6110-0000 3002e-0000e 0(10)01e-0000e 4600e-0000e 0(10)21e-0000e 6110-0000 3710e-0000e 1801e-0000e 4221e-0000e 0(10)00e-0000e 0(11)11-0110 3112-0110 2312-0110 0(11)11-0110 4710-0110 5111-0110 5510f-0110f 5111-0110 3202e-0200e 3222-0220 4002e-1000e 4002e-0200e 2422-0220 3202e-1000e 3202e-0200e 5201e-1000e 5201e-0200e 5221-0220 6001e-1000e 5221f-0220f 6001e-1000e 3312-0310 3332f-0330f 4112-0310 4112-1110 2532f-0330f 3312e-0310e 3312-1110 0(13)1-0310 5331f-0330f 6111-1110 3003e-0001e
7985.547 8168.568 8284.800 8364.729 8548.772
3002/2202 4201/1801/2601 5001/3401/2601 5001/4201/3401 3112/2312
68/21 34/24/17 38/23/21 40/24/16 54/31
3002e-0000e 4201e-0000e 5001e-0000e 5001e-0000e 3112-0110
14 14 14 14 14
7918.579 7999.429 8070.796 8197.358 8292.122 8580.757 8761.411 8875.579
3002/1402 3002/2202 0(10)01/4201 1801/5001 5001 2312/3112/1512 5111/1911/3511/0(11)11 5111/1911
31/30 36/29 28/27 21/20 36 34/27/18 26/18/17/17 27/19
3002e-0000e 3002e-0000e 0(10)01e-0000e 5001e-0000e 5001e-0000e 2312-0110 5111-0110 5111f-0110f
14 14 14 14 14 14 14 14
8020.659
2202/3002/1402
36/35/22
2202-0000
14
48/41 56/20
3002e-0000e 5001e-0000e
14 14
a b c
7966.347 8132.502
2
0
2
0
30 2/22 2 5001/2601
2
25/19/18 2
Cluster labeling notation: (P¼ 2V1 þ V2 þ 4V3, l2,i): i is the order number within the cluster increasing with the energy. Squares of the expansion coefficients of the vibrational state for the dominant basis states appearing in the preceding column. V1V2ℓ2 V 3 , V2 is is given between parentheses when it is larger than 10.
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Fig. 4. Overview comparison between the transitions of 14N216O, 15N14N16O, 14N15N16O, 14N218O and 14N217O assigned in the CRDS spectrum of nitrous oxide in natural isotopic abundance between 7915 and 8334 cm 1 (right panels) and the corresponding spectra predicted in the frame of the effective operator approach [10–12] (left panels).
that most of the unassigned lines are due to N2O isotopologues. A summary of the observations is presented in Table 1 which gives the HITRAN notation of the various isotopologue species and the corresponding “natural” isotopic abundances as given in Ref. [17] and adopted in the HITRAN database. Five nitrous oxide isotopologues were found to contribute to the spectrum: 14N216O, 14N15N16O, 15 14 16 N N O, 14N218O and 14N217O. A total of 3322 transitions belonging to 64 bands were assigned. For comparison, only 13 bands were previously measured by Fourier Transform spectroscopy in the studied region. Note that in our region, no data are provided by the HITRAN database for N2O. All identified bands belong to the ΔP ¼ 13 and 14 series of transitions, where P¼2V1 þV2 þ4V3 is the polyad number
(Vi are vibrational quantum numbers). Among the 48 bands of 14N216O which were measured, 45 are ΔP ¼14 bands. The used rovibrational EH models are based on a polyad structure resulting from the approximate relations between the harmonic frequencies ω3 2ω1 4ω2 . As the mixing between the ðV 1 V 2 l2 V 3 Þ states may be strong, the vibrational states are preferably labeled using the (P, l2, i) triplet where the index i increases with the energy. The vibrational labeling and the dominant basis states in the vibrational decomposition of the upper states of the various bands are listed in Table 2. Note that the same ðV 1 V 2 l2 V 3 Þ state may be dominant in the eigenfunction expansion of different vibrational states.
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41
constants have been fixed to the literature values [20,21]. The global line list provided as Supplementary material includes for each band, the fitted spectroscopic parameters of the upper state with the corresponding errors (in % and cm-1), lower state parameters and rms values of the fit together with the observed and calculated values for the line positions. 14
Fig. 5. Overview comparison of the CRDS observations of 14N216O transitions between 7915 and 8334 cm 1 with the observations available in the literature [7–9]. On the upper panel, literature observations (blue) are superimposed on the line list predicted using the effective operator approach [6,10] (gray). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Overall, 2640 transitions belonging to 48 bands were assigned to the main isotopologue. The overall list is shown in Fig. 5 where the previous observations by Fourier Transform Spectroscopy are highlighted [7–9]. The line intensities of the literature data were calculated using the set of effective dipole moment parameters of Ref. [6]. Fig. 5 illustrates that the present results considerably extend the observations in the region. Among the 48 14 N216O bands presently analyzed, only 7 were previously reported from Campargue et al. [7], Weirauch et al. [8], and Wang et al. [9] who used FTS associated with a multipass cell. Among the 48 bands analyzed, 33 are hot bands. The most excited upper level observed in this study is the (3003) state at 10163.6 cm 1 which belongs to the P¼ 18 polyad observed through the (3003)–(0001) hot band (ΔP ¼14) at 7939.8 cm 1. The constants retrieved from the fit of the line positions are listed in Table 3. The rms values of the (obs.-calc.) deviations are generally smaller than 1.0 10 3 cm 1 which is consistent with the uncertainty on the line positions. As marked in Table 4, six bands were found to be affected by perturbation, the corresponding perturbed positions were excluded from the fit. The perturbations will be analyzed in the next section. 14
Fig. 4 shows an overview comparison between the observations and the predicted spectra for the five studied nitrous oxide isotopologues. The experimental line list provided as Supplementary material includes the experimental and EH calculated positions and intensities for each line, together with corresponding rovibrational assignments. 3.2. Band by band rotational analysis In the case of unperturbed bands, the rotational analysis was performed using the standard equation for the vibration-rotation energy levels: F v ðJÞ ¼ Gv þ Bv JðJ þ 1Þ Dv J 2 ðJ þ1Þ2 þH v J 3 ðJ þ 1Þ3 ;
ð2Þ
where Gν is the vibrational term value, Bv is the rotational constant, Dv and Hv are centrifugal distortion constants. The spectroscopic parameters for an upper state were fitted directly to the observed line positions of the respective bands, and in the case of hot bands involving e and f rotational sublevels, the ee, ef, fe and ff sub bands were considered independently. The lower state rotational
N216O
N15N16O and
15
N14N16O
On the basis of the effective Hamiltonian models, a total of 212 and 331 transitions belonging to 5 and 8 bands were rovibrationally assigned for the 14N15N16O and 15N14N16O isotopologues, respectively. The previous observations in this region are limited to three bands detected for both 14 15 16 N N O [18] and 15N14N16O [19] from FTS spectra of N2O samples highly enriched in 15N. The detection of new bands of these minor isotopologues from spectra of a sample with natural isotopic abundance (3.64 10 3 for 14 15 16 N N O and 15N14N16O) illustrates the sensitivity of the present CRDS recordings. The retrieved spectroscopic constants of the 14N15N16O and 15N14N16O bands are included in Table 3. 14
N218O and
14
N217O
Two 14N218O bands and one 14N217O band were assigned in the 7915–8334 cm 1 region. The corresponding spectroscopic parameters are included in Table 3. To our knowledge, no bands of these two minor isotopologues were previously reported in the region.
42
Table 3 Spectroscopic parameters (in cm-1) for the different bands of the N2O isotopologues assigned in the CRDS spectrum between 7915 and 8334 cm 1. Lower state constants [20,21] V1V2 l2 V3a (P l2 i)b
Bv
Dv 107
(0 0 1) (1 1 1) (1 1 1) (2 2 2) (2 2 2) (2 0 1) (2 0 2) (3 3 2) (3 3 2) (3 1 1) (3 1 1) (3 1 2) (3 1 2) (4 0 1)
0.0 585.76787 585.76787 1177.74467 1177.74467 1168.13230 1284.90334 1766.91238 1766.91224 1749.06523 1749.06515 1880.26574 1880.26574 2223.75677
0.419011001 0.419177925 0.419969845 0.420125256 0.420126260 0.419920952 0.417255210 0.420667053 0.420671366 0.419583944 0.421079073 0.417464677 0.418372995 0.41555951
1.7609193 1.783245 1.793030 1.196792 1.818000 2.491945 1.726978 1.617863 1.683740 2.110353 2.177366 1.748503 1.719561 1.754675
(0 0 1) (1 1 1) (1 1 1)
0.0 575.43365 575.43365
0.418981810 0.419108916 0.419918641
1.763264 1.785826 1.794459
(0 0 1) (1 1 1) (1 1 1)
0.0 585.31212 585.31212
0.404857965 0.405037265 0.405781109
1.642938 1.656798 1.667421
(0 0 1)
0.0
0.406672154
1.663972
(0 0 1)
0.0
0.395577895
1.583456
Upper state constants V1 V2 l 2 V3 (P l2 i)
Gv
Bv
Dv 107
Hv 1012
ν0 c
Observed linesd
n/Ne
rmsf
Noteg
7993.34685(35) 7998.58422 (32) 8001.6829(50) 8015.47628(84)
0.4164357(47) 0.4094513(26) 0.416633(19) 0.4103267(24)
7.470(47) 2.165(13) -4.01(21) 1.492(16)
5.1(14) 0.26(17) -11.1(74) 2.20(30)
7993.34685(35) 7998.58422 (32) 8001.6829(50) 8015.47628(84)
1
0.4147315(14) 0.40718738(37) 0.4147647(49) 0.4194873 (56) 0.4148232(31) 0.4130802(64) 0.4106505(16) 0.4107807(26) 0.41158761(60)
2.4801(79) 1.3814(15) 16.01(30) 10.48(21) 1.0355(93) 1.703(95) 1.609(10) 0.777(11) 3.3706(70)
22/80 29/109 18/18 28/66 /4 18/18 68/68 33/80 36/55 27/27 11/12 10/10 14/18 62/62
0.88 0.93 0.90 0.97
8046.34910(42) 8083.95210(29) 8145.54283(19) 8148.86459(35) 8156.7034(24) 8159.65991(76) 8159.66173(32) 8266.2887(12) 8276.32336(12)
P49/R46h P59/R69 P39/R37 P60/R58 P9/R4 Q42 P76/R74 P58/R56 P52/R47 P50/R46 Q25 P40/R19 P46/R40 P48/R46
446 0000e 0110e 0110f 0220e 0220f 0200e 1000e 0330e 0330f 0310e 0310f 1110e 1110f 0001e 456 0000e 0110e 0110f 546 0000e 0110e 0110f 447 0000e 448 0000e
446 cold bands 0(10)01e-0000e 1402e-0000e 0(10)21e-0000e 2222e-0000e 6110e-0000e 6110f-0000e 3002e-0000e 0(10)01e-0000e 4600e-0000e 0(10)21e-0000e 6110f-0000e 6110e-0000e 3710e-0000e 1801e-0000e
(14 (14 (14 (14 (13
0 7) 0 8) 2 14) 2 15) 1 14)
(14 (14 (14 (14 (13
0 9) 0 10) 0 11) 2 20) 1 15)
(13 1 16) (14 0 12)
Hv 1012
0.016529 -0.01714 -0.01766 -2.9502 0.095 2.955393 0.146666 -0.99132 3.0154 1.2225 -0.35921 0.1075 0.21746 -0.013626
0.18666
2.451(18) 83(49) -11(21)
10.13(22)
8046.34910(42) 8083.95210(29) 8145.54283(19) 8148.86459(35) 8156.7034(24) 8159.65991(76) 8159.66173(32) 8266.2887(12) 8276.32336(12)
0.80 0.57 0.44 0.85 0.83 0.73 0.52 0.97 0.40
Previous observations
[7-9] 2
[7-9] [9] 3
[7,8]
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
Gv
Table 3 (continued) Lower state constants [20,21] V1V2 l2 V2a (P l2 i)b
Dv 107
Hv 1012
(14 2 22) (14 0 13) (14 0 14)
8294.11739(69) 8319.79197(43) 8376.5133(99)
0.4123693(18) 0.4178009(68) 0.4087782(66)
0.802(12) 12.10(14) 1.651(11)
-7.62(25)
(17 1 11)
9783.7782(19) 9783.7755(17) 9660.96801(38) 9660.97051(61) 9683.90759(29) 9219.05571(15) 10163.59545(40) 9108.32288(30) 9121.24198(24) 9121.24221(33) 8547.4981(16) 8547.51423(59) 8559.181447(96) 8559.181486(99) 9783.77001(52) 9783.77524(51) 9219.05535(22) 9244.55748(28) 9244.55778(31) 9884.69602(44) 9884.69664(44) 9294.99312(14) 9820.50949(31) 8663.15873(13) 8663.15841(14) 9398.81683(36) 8701.40887(45) 8701.40852(38) 8704.53286(38) 8704.53199(47) 9294.99391(15) 9884.69521(58) 10087.19593(70) 10087.20153(50) 9958.36342(37) 9958.36306(49) 9983.56550(46) 9398.81679(27) 9517.87355(23) 9412.96666(20) 9412.96644 (70) 8843.44953(13) 8843.44918(12)
0.4074100(43) 0.4091847(39) 0.4094924(17) 0.4117314(40) 0.4113722(18) 0.40751333(55) 0.4037158(22) 0.4103255 (29) 0.4107223(11) 0.4107332(20) 0.4149867(68) 0.4185094(54) 0.40928782(89) 0.4109353(12) 0.4074356(29) 0.4091792(26) 0.4075138(10) 0.4090108(12) 0.4090026(26) 0.4063890(17) 0.40792903(99) 0.40619595(59) 0.4097662(12) 0.40757302(37) 0.40880364(37) 0.4120047(30) 0.4138747(57) 0.4173748(72) 0.4166077(51) 0.4212481(79) 0.40618789(57) 0.4063840(46) 0.4087266(51) 0.4113240(20) 0.4106953(13) 0.4138795(19) 0.4130550(19) 0.4120056(14) 0.4094449(33) 0.4125132(11) 0.4125117 (15) 0.41075199(46) 0.41324693(56)
1.909(21) 1.965(19) 1.991(15) 1.119(26) 1.720(24) 2.3511(36) 1.392(22) 4.540(42) 0.5123(78) 1.545(29) 4.093(50) 3.92(17) 2.108(19) 2.158(31) 2.094(31) 1.910(23) 2.364(10) 1.218(12) 0.514(44) 1.325(14) 0.8276(49) 0.9108(57) 1.4593(87) 1.4801(23) 1.2914(22) 5.111(52) 13.25(16) 24.52(33) -4.17(17) -1.43(34) 0.7736(36) 1.190(67) 2.440(52) 2.374(17) 2.9613(84) 3.310(14) 1.536(15) 5.120(17) 3.02(12) -0.266(13) 2.4122(69) 2.4580(35) 2.6230(55)
10196.7322(16)
0.407339(37)
1.5(13)
(17 1 10) (17 3 18) (16 0 11) (18 0 9) (16 0 10) (16 2 18) (15 1 7) (15 1 8) (17 1 11) (16 0 11) (16 2 20) (17 1 14) (16 0 14) (17 3 22) (15 1 9) (16 0 15) (15 1 10) (15 1 11) (16 0 14) (17 1 14) (17 1 17) (17 1 15) (17 3 27) (16 0 15) (16 0 17) (16 2 27) (15 1 12) (15 1 13) (17 1 19)
11.12(82) 2.624(59) 90.1(17) 13.9(11) -8.99(81) 23.4(11) 49.8(23)
3.24(26) -3.87(34) -9.3(21)
5.68(15) 0.985(39) 1.684(36) 23.1(23) 43(13) 13(40)
23.51(57) 15.03(11) -20.57(36) 2.956(68) 1.22(14)
8294.11739(69) 8319.79197(43) 8376.5133(99)
P56/R52 P23/R11 P63
7903.51246(19) 7903.50976(17) 7911.90278(38) 7911.90536(61) 7916.99535(29) 7934.15237(15) 7939.83868(40) 7940.19058(30) 7943.49731(24) 7943.49754(33) 7961.73023(16) 7961.74636(59) 7973.413577(96) 7973.413616(99) 8034.70478(52) 8034.71009(51) 8050.92305(22) 8066.81281(28) 8066.81311(31) 8004.43028(44) 8004.43090(44) 8010.08978(14) 8053.59725(31) 8077.39086(13) 8077.39054(14) 8113.91349(36) 8115.64100(45) 8115.64065(38) 8118.76499(38) 8118.76412(47) 8126.86161(15) 8135.62998(58) 8206.93019(70) 8206.93579(50) 8209.29819(37) 8209.29791(49) 8216.65326(46) 8230.68449(27) 8232.97021(23) 8235.22199(20) 8235.22177(70) 8257.68166(13) 8257.68131(12) 8292.51684i 8316.46646(16)
R39 R40 R33 R37 R44/Q11 P18/R65 P21/R31 P23/R41 P20/R39 P25/R42/Q16 P35/R41 P46/R49 P43/R52/Q31 P40/R69/Q36 P31/R32 P34/R30 P53/R24 P50/R50 P54/R53/Q19 P37/R31 P46/R34 P53/R52 P39/R33 P66/R65/Q28 P66/R66/Q22 P31/R38 P40/R56 P47/R56 P28/R33 P21/R37 P37/R41 P29/R16 P19/R29 P33/R30 P40/R31 P33/R36 P37/R31/Q9 P47/R39 P27/R24 P53/R44/Q06 P45/R44 P64/R43/Q14 P52/R51/Q22 P14/R13 P9/R14
35/38 15/16 9/9
0.65 0.93 0.56
13/13 12/12 25/25 11/11 31/32 55/60 21/22 35/63 45/52 27/34 5/8 14/43 81/103 68/98 20/29 20/22 43/43 55/62 34/64 30/35 31/35 78/85 33/33 100/105 83/86 29/29 37/66 34/69 24/30 21/33 48/52 11/11 9/13 16/21 19/25 18/23 16/20 49/54 33/35 41/47 26/28 70/78 72/73 /5 5/6
0.74 0.82 0.79 0.91 0.67 0.63 0.77 0.87 0.89 0.71 0.86 0.59 0.36 0.30 0.94 0.98 0.68 0.82 0.74 0.98 0.82 0.57 0.75 0.60 0.59 0.82 0.99 0.73 0.66 0.58 0.57 0.69 0.81 0.61 0.71 0.89 0.72 0.78 0.43 0.71 0.96 0.57 0.46
[7-9]
4
5
[9]
[9]
6
7 0.69
43
Bv
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
4221e-0000e 0(10)01e-0000e 5001e-0000e 446 hot bands 4112e-1110e 4112f-1110f 3312e-0310e 3312f-0310f 3332f-0330f 4002e-1000e 3003e-0001e 3202e-0200e 3222e-0220e 3222f-0220f 0(11)11e-0110e 0(11)11f-0110f 3112e-0110e 3112f-0110f 4112e-0310e 4112f-0310f 4002e-0200e 2422e-0220e 2422f-0220f 3312e-1110e 3312f-1110f 3202e-1000e 2532f-0330f 2312e-0110e 2312f-0110f 5201e-1000e 0(11)11e-0110e 0(11)11f-0110f 4710e-0110e 4710f-0110f 3202e-0200e 3312e-0310e 6111e-1110e 6111f-1110f 0(13)11e-0310e 0(13)11f-0310f 5331f-0330f 5201e-0200e 6001e-1000e 5221e-0220e 5221f-0220f 5111e-0110e 5111f-0110f 5111f-0110f 6111e-1110e
Gv
10196.7333(14) 9606.33195(49) 8959.7701(34) 8959.7743(44)
0.409863(35) 0.4072714(67) 0.4089578(35) 0.4109677(40)
8.5(16) 2.64(22) 1.7264(84) 1.5586(77)
23.22(21)
(16 2 31) (14 (14 (14 (14
0 0 0 0
P14/R11 P28/R14 P55 P62 P37
8/9 20/20 15/16 7/9 /3
0.83 0.79 0.75 0.79 7
7985.54740(13) 8168.56879(28) 8284.80042(40) 8364.729(10)
0.40680698(26) 0.4117992(17) 0.4092324(49) 0.407048(15)
1.60124(93) 4.109(21) 3.15(14) 0.941(51)
7985.54740(13) 8168.56879(28) 8284.80042(40) 8364.729(10)
P49/R56 P31/R26 P30/R25 P42
74/81 27/31 27/29 5/6
0.59 0.64 0.78 0.25
(15 1 9)
8548.77283(25) 8548.77395(32)
0.40715562(83) 0.4082247(12)
1.6419(50) 1.5125(73)
7973.33918(25) 7973.34030(32)
P42/R17 P43/R24
24/29 32/36
0.53 0.88
(14 (14 (14 (14 (14
7918.57979 (29) 7999.42965(24) 8070.79646(96) 8197.35893(21) 8292.12259(22)
0.3958297 (42) 0.39385942(89) 0.4002022(55) 0.39766238(60) 0.39536948(96)
4.06(13) 1.1521(78) 5.319(77) 2.6807(32) 1.7302(97)
7918.57979 (29) 7999.42965(24) 8070.79646(96) 8197.35893(21) 8292.12259(22)
P03/R60 P56/R49 P41/R10 P34/R46 P54/R34
36/91 68/70 15/16 32/33 49/52
0.77 0.80 0.94 0.69 0.74
(15 1 14)
8580.75754(27) 8580.75759(29) 8761.41178(67) 8761.41762(63) 8875.57976(24)
0.39419944(77) 0.3954211(12) 0.3970618(37) 0.3993389(20) 0.3975009(15)
1.3017(41) 1.1031(96) 2.267(42) 2.296(12) 1.407(16)
7995.44542(27) 7995.44547(29) 8176.09966(67) 8176.10550(63) 8290.26764(24)
P47/R38 P37/R33 P25/R28 P42/R28 P31/R23
34/39 22/26 15/16 13/15 9/9
0.82 0.62 0.85 0.99 0.29
(14 0 9)
8020.65912(15)
0.3958322(12)
1.034(16)
8020.65912(15)
P28/R25
33/33
0.41
(14 0 9) (14 0 14)
7966.34701(18) 8132.50292(15)
0.3858295(66) 0.38794035(76)
0.6444(45) 2.5375(75)
7966.34701(18) 8132.50292(15)
P41/R37 P29/R33
62/62 44/44
0.69 0.48
0 0 0 0 0
9) 12) 14) 15)
8316.46756(14) 8321.42861(49) 8374.00223(34) 8374.00643(44) 8365.14736i
7) 9) 10) 12) 14)
(15 1 9) (15 1 12)
10(11) 2.29(18) 42.6(30) 5.67(25)
[18] [18] [18]
8
[19] [19]
[19]
V1V2l2V3 correspond to the maximum value of the modulo of the expansion coefficients of the eigenfunction. V2 is given between parentheses when it is larger than 10. Cluster labeling notation: (P¼ 2V1 þV2 þ 4V3, l2,i): i is the order number within the cluster increasing with the energy. c ν0 is the band center. d Observed branch with the maximum value of the total angular momentum quantum number. e n is number of transitions included in the fit; N is number of assigned transitions. f Root Mean Squares of residuals of the spectroscopic parameters fit is given in 10-3 cm-1. g Notes: 1. Intrapolyad resonance anharmonic interaction between (14 0 7)–(14 0 8) (energy levels crossing at J¼ 29). 2. Intrapolyad resonance anharmonic interaction between (14 2 14)–(14 2 15) (energy levels crossing at J¼ 45). 3. Interpolyad resonance Coriolis interaction between (14 0 11)–(13 1 15) (energy levels crossing at J¼ 38). Intrapolyad resonance anharmonic interaction between (14 0 10)–(14 0 11). 4. Intrapolyad resonance anharmonic þl-type interaction (16 0 10)–(16 2 16) (energy levels crossing at J¼26). 5. Intrapolyad resonance anharmonic interaction between (15 1 7 )–(15 1 8) (energy levels crossing at e:J ¼46, f:J ¼40). 6. Interpolyad resonance Coriolis interaction (15 1 10)–(16 0 1) (energy levels crossing at J¼ 35). Intrapolyad resonance anharmonic interaction (15 1 10)–(15 1 11). 7. A few lines. Not fitted. 8. Intrapolyad resonance anharmonic þ l-type interaction (14 0 7)–(14 2 11) (energy levels crossing at J ¼48). Intrapolyad resonance anharmonic interaction (14 0 7)–(14 0 6) (energy levels crossing at J ¼35). h The input data set of this band located near the low energy border of the investigated region was complemented with line positions previously reported in Ref. [4]. The added line positions are indicated in the Supplementary material. i Band center as provided by the global effective Hamiltonian. b
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
a
(16 0 19) (15 1 14)
44
6111f-1110f 6001e-1000e 5111e-0110e 5111f-0110f 5221f-0220f 456 cold bands 3002e-0000e 4201e-0000e 5001e-0000e 5001e-0000e 456 hot bands 3112e-0110e 3112f-0110f 546 cold bands 3002e-0000e 3002e-0000e 0(10)01e-0000e 5001e-0000e 5001e-0000e 546 hot bands 2312e-0110e 2312f-0110f 5111e-0110e 5111f-0110f 5111f-0110f 447 cold band 2202e-0000e 448 cold bands 3002e-0000e 5001e-0000e
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
4. Discussion 4.1. Comparison with the effective Hamiltonian predictions An overview comparison of the differences between the measured line positions and their predicted values [10–12] are plotted versus the wavenumber in Fig. 6. This plot illustrates the good predictive ability of the effective Hamiltonian model for 14N216O, 15N14N16O and 14N15N16O. The majority of the residuals lies between 0.03 and 0.05 cm-1. However, the line positions of the (14 0 11)– (0 0 1), (18 0 9)–(4 0 1) and (15 1 11)–(1 1 1) 14N216O bands – (4600-0000), (3003-0001) and (4710-0110) in normal mode notation- are found systematically shifted from their predicted values by values between 0.1 and 0.25 cm-1. The newly measured line positions will therefore help to significantly improve the set of the effective Hamiltonian parameters of the main isotopologue.
45
absent in the preliminary effective Hamiltonians developed for these isotopologues [12]. As a result, the deviations of the measured positions from their predicted values range between -2.0 and -1.0 cm-1 for the two bands of the 14N218O isotopologue and are about -10.5 cm-1 for the 2202e-0000e band of the 14N217O isotopologue (Fig. 6). 4.2. Rovibrational perturbations Six bands of 14N216O and the 3ν1+2ν3 band of 15N14N16O were found to be affected by perturbations which obliged us to exclude a significant number of line positions from the input data used to derive the spectroscopic constants (see Table 3). Table 4 lists for each of the perturbed band, the coupling mechanism and the J values corresponding to the energy crossing of the interacting states. When the perturbation is due to a coupling between vibrational states belonging to the same polyad, it is generally satisfactorily reproduced by the EH model but in the case of interpolyad interactions (Coriolis or anharmonic), the line positions calculated from the effective Hamiltonian or from the spectroscopic parameters (Table 3) deviate in a similar way from the measured values. The perturber and interaction mechanism of an interpolyad coupling can nevertheless be identified from the energy crossing predicted by the effective Hamiltonian model.
Fig. 6. Differences between the line positions of 14N216O, 14N15N16O, 15 14 16 N N O, 14N218O and 14N217O measured by CRDS between 7915 and 8334 cm-1 and their values predicted with the respective effective Hamiltonians. On the upper panel for the (15 1 11)–(1 1 1), (18 0 9)–(4 0 1) and (14 0 11)–(0 0 1) 14N216O bands are highlighted with triangles, rhombs and squares, respectively.
Due to a lack of the input experimental information, larger deviations are observed for the 14N218O and 14N217O isotopologues because many important parameters are
Fig. 7. Intrapolyad resonance anharmonic interaction between the (14 0 7) and the (14 0 8) upper states of 14N216O observed through the 0(10)01e-0000e and 1402e-0000e cold bands. Left hand and right hand panels show the spectrum predicted by the effective operator approach and the CRDS line lists, respectively.
46
E.V. Karlovets et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 169 (2016) 36–48
Table 4 Observed perturbations of the N2O bands between 7915–8334 cm 1. Band affected
Interaction mechanism
Jcrossa
14
0(10)01-0000 1402-0000 2222-0000 4600-0000 3202-0200 3112-0110 0(11)11-0110
29 29 45 38 26 e:46 and f:40 35
15
3002-0000
Intrapolyad anharmonic (14 0 7)–(14 0 8) Intrapolyad anharmonic (14 0 8)–(14 0 7) Intrapolyad anharmonic (14 2 14)–(14 2 15) Interpolyad Coriolis (14 0 11)–(13 1 15) Intrapolyad anharmonicþ l-type (16 0 10)–(16 2 16) Intrapolyad anharmonic (15 1 7)–(15 1 8) Interpolyad Coriolis (15 1 10)–(16 0 1) þIntrapolyad anharmonic (15 1 10)–(15 1 11) Intrapolyad anharmonicþ l-type (14 0 7)–(14 2 11) þIntrapolyad anharmonic (14 0 7)–(14 0 6)
Isotopologue N216O
N14N16O
a
48 35
Value of the angular momentum quantum number at which the energy level crossing takes place.
Below we discuss in more details some of the perturbations observed for the 14N216O and 15N14N16O isotopologues. The (14 0 7) and (14 0 8) states of 14N216O are in intrapolyad anharmonic interaction. These states were observed through the 0(10)01e-0000e and 1402e-0000e cold bands at 7993.34 and 7998.58 cm-1, respectively, and are found perturbed for J values around 29. Fig. 7 shows the impact of this interaction on the rotational distribution of the 0(10)01e-0000e band and the strong intensity transfer to the 1402e-0000e band near the energy crossing. The reduced energy plot of Fig. 8 shows the energy crossing of the two interacting states.
Fig. 9. Differences between the measured values of the transition wavenumbers of the 3202e-0200e band of 14N216O at 7940.2 cm-1 ((16 0 10) upper state) and the corresponding values calculated using the EH model (upper panel) and the spectroscopic parameters of Table 3 (lower panel) versus m (where m¼ J for P-branch and m¼Jþ 1 for R-branch). The (16 0 10) upper state is perturbed by the resonance anharmonic þl-type interaction with the (16 2 16) state. Note the different ordinate scale.
Fig. 8. Reduced energy plot for the (14 0 7)–(14 0 8) interacting system of 14 N216O. Differences between the measured values of the transition wavenumbers of the bands: 0(10)01e-0000e at 7993.3 cm 1 ((14 0 7) upper state) and 1402-0000e at 7998.5 cm-1 ((14 0 8) upper state), and the corresponding values calculated using the (14 0 8) spectroscopic parameters (Table 3). For each Jupper value, the values corresponding to the R(Jupper-1) (open circle) and P(Jupper þ 1) (full circle) transitions are plotted. The (14 0 7) and (14 0 8) upper states are in intrapolyad anharmonic interaction (energy levels crossing at J ¼29).
The (16 0 10) upper state of 14N216O – (3202) in normal mode notation – is perturbed by a resonance anharmonicþ l-type interaction with the (16 2 16) state belonging to the same P¼16 polyad. Fig. 9 shows the differences between the measured values of the transition
wavenumbers of the 3202e-0200e band at 7940.2 cm 1 and the corresponding values calculated using the EH model and the spectroscopic parameters of Table 3. Near the crossing point at J ¼26, the shifts of the line positions from their unperturbed values calculated using the band parameters, reach values up to 0.1 cm 1 while they are satisfactorily predicted by the EH model. The (18 0 9) upper state of 14N216O – (3003) in normal mode notation – is affected by interpolyad resonance anharmonic interaction with (16 0 25) vibrational state. The energy level difference is about 6.5 cm 1 at J ¼0 and increases with the angular momentum quantum number J. So the perturbation is smooth and could be accounted for by the effective values of the spectroscopic constants. But
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in the case of the global effective operators approach the resonance interaction terms should be considered explicitly. The matrix elements of the respective resonance interaction operators are listed in our paper [1]. The used polyad model of effective Hamiltonian does not take into account these terms. Because of this the line positions of the 3003-0001 band are about of -0.1 cm 1 off the experimental values. In the case of the 15N14N16O isotopologue, the 3002e0000e band ((14 0 7) upper level) is affected by two intrapolyad interactions: an anharmonicþl-type interaction with the (14 2 11) state and an anharmonic interaction with the (14 0 6) state. The interaction mechanism, the perturber state and the J value of the angular momentum quantum number corresponding to the energy crossing could be identified using the EH predictions of Ref. [11] (Table 4).
5. Conclusion Sixty four, mostly new, bands of five nitrous oxide isotopologues (14N216O, 14N15N16O, 15N14N16O, 14N218O and 14 N217O) have been rovibrationally assigned in the high sensitivity CRDS spectrum of natural nitrous oxide between 7915 and 8334 cm 1. The assignment procedure based on the predictions of the EH models was a laborious task as a result of the high density of the observed transitions and of the superimposition of the spectra of five N2O isotopologues together with impurity lines. Most of the measured transitions belong to weak hot bands of 14 N216O. The predicted line positions show an overall good agreement with the observations for the main isotopologue (maximum deviation of about 0.2 cm 1) but discrepancies increase and reach values larger than 1 cm-1 for the minor isotopologues. A few resonance perturbations were identified. They include a strong intrapolyad anharmonic interaction between the (14 0 7) and the (14 0 8) upper states of 14 N216O observed through the 0(10)01e-0000e and 1402e0000e cold bands and two interpolyad Coriolis resonance interactions which are not taken into account by the polyad model of effective Hamiltonian. The observed new data will be valuable for the refinement of the effective Hamiltonian parameters that will lead to the improvement of the quality of the prediction of the N2O line positions and intensities. The development of a non-polyad effective Hamiltonian which is in progress at IAO (Tomsk), should help us to decrease the rms deviation and assign part of the lines left unassigned in our CRDS spectra. Indeed, in all our analysis of the CRDS spectrum of nitrous oxide [1–6], a significant fraction of weak lines (about 30 %) was left unassigned. We believe that most of them are due to N2O isotopologues. Our assignment procedure rely mostly on the EH predictions, the failure to assign these lines may indicate that some important improvements are still needed in the modeling. Line intensities may provide valuable insights for the assignment of the remaining lines which are all weak or very weak. As illustrated in Fig. 7, the present status of the line intensity modeling based on the measurements of Ref. [6] is not fully satisfactory when extrapolated to the weak bands unobserved in Ref. [6], because some important dipole
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moment parameters are unknown. For instance, some bands predicted with intensity largely above the CRDS sensitivity threshold were not detected, indicating that the corresponding predicted intensities are overestimated. The refinement of the global effective operators in particular of the ΔP¼ 13 and 14 effective dipole moment parameters, for the various nitrous oxide isotopologues will be the subject of the next contribution. In addition, the line positions of the newly measured bands of 14N218O and 14N217O will be used to refine the parameters of the effective Hamiltonians of the respective isotopologues. We hope that these improvements will help to further extend the assignments in the present spectrum.
Acknowledgments This work is jointly supported by CNRS (France) and RFBR (Russia) in the frame of the International Associated Laboratory SAMIA. This project takes place in the frame of the LabexOSUG@2020 (ANR10 LABX56).
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j. jqsrt.2015.09.012.
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