FTIR spectrometer with 30 m optical cell and its applications to the sensitive measurements of selective and nonselective absorption spectra

Journal of Quantitative Spectroscopy & Radiative Transfer 177 (2016) 253–260

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FTIR spectrometer with 30 m optical cell and its applications to the sensitive measurements of selective and nonselective absorption spectra Yu.N. Ponomarev a,b, A.A. Solodov a,b, A.M. Solodov a, T.M. Petrova a, O.V. Naumenko a a b

V.E. Zuev Institute of Atmospheric Optics SB Russian Academy of Sciences, 1, Academician Zuev's Square, 634021 Tomsk, Russia National Research Tomsk State University, Lenina Av. 36, Tomsk 634050, Russia

a r t i c l e i n f o

abstract

Article history: Received 31 October 2015 Received in revised form 9 February 2016 Accepted 19 February 2016 Available online 26 February 2016

A description of the spectroscopic complex at V.E. Zuev Institute of Atmospheric Optics, SB RAS, operating in a wide spectral range with high threshold sensitivity to the absorption coefficient is presented. Measurements of weak lines and nonselective spectra of CO2 and H2O were performed based on the built setup. As new application of this setup, positions and intensities of 152 weak lines of H2O were measured between 2400 and 2560 cm
1 with threshold sensitivity of 8.6  10
10 cm
1, and compared with available calculated and experimental data. Essential deviations between the new intensity measurements and calculated data accepted in HITRAN 2012 and GEISA 2015 forthcoming release are found. & 2016 Elsevier Ltd. All rights reserved.

Keywords: High resolution FTIR spectroscopy Weak absorption lines Nonselective absorption H2O spectra CO2 spectra

1. Introduction Accurate data on the molecular high-resolution absorption spectra of atmospheric constituents from the microwave to the near ultraviolet are of great importance for modeling and understanding of many fields in environmental sciences, chemistry and physics. A detailed knowledge of the spectral line parameters is important for a great many applications like astrophysics, planetary and stellar atmospheres, industrial processes, investigation of molecular interactions. Characterization of weak lines and nonselective (continual) absorption is particularly needed in the atmospheric transparency windows, for the calculation of optical and laser radiation propagation in the atmosphere, for evaluation of the balance of incoming solar radiation, the remote sensing and development of the climatic models [1–4]. One way to enhance the sensitivity threshold to absorption coefficient is the increase of optical path length. This can be achieved in multipass http://dx.doi.org/10.1016/j.jqsrt.2016.02.026 0022-4073/& 2016 Elsevier Ltd. All rights reserved.

cells which are used for observing spectra that are very weak. The studies of broadband high-resolution absorption spectra of molecular gases in a wide spectral range are mainly performed using Fourier transform spectrometers. However, serial cells designed for FTIR spectrometers have several tens of meters optical path length, which provides the sensitivity threshold about 10
6 cm
1. In order to increase the sensitivity of Fourier transform spectrometers in a high-frequency range (higher than 10,000 cm
1) the LEDs (light-emitting diode) as sources can be used [5]. The radiation power of LEDs in narrow spectral regions is approximately two orders of magnitude higher than standard halogen lamps have. Under equal conditions the use of LEDs in Fourier transform spectrometers for spectra recording significantly increases the signal-to-noise ratio. For example, the application of this method in [6] allowed detecting of CO2 absorption spectra within 11,400– 11,510 cm
1 interval with a sensitivity of 10
8 cm
1.

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Yu.N. Ponomarev et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 177 (2016) 253–260

However, in the middle- and far IR regions sufficiently powerful LEDs are still absent. In these spectral ranges there are many spectroscopic problems which cannot be solved using commercial absorption cells with short optical paths. For example, when studying the continuum absorption, deviations of the amplitude and form of the signal passing through a cell are the primary source of errors; this is the so-called problem of the base line [7–10]. As the length of the optical path increases the error connected with the base line instability reduces; therefore, more accurate results can be obtained when the Fourier transform spectrometers with long-base multipass cells are used. In this paper we present the description of experimental optical complex, based on a Bruker IFS 125 HR Fourier transform spectrometer and 30-m gas cell equipped with the White-type multipass system which has been operating in the V.E. Zuev Institute of Atmospheric Optics SB RAS (IAO SB RAS) since 2011. The applications of the described instrumentation to study of selective and continual absorption spectra of atmospheric gases are discussed.

2. Experimental complex The FTIR spectrometer is equipped with several light sources, detectors and beamsplitters, and, therefore, it can operate in a wide spectral region, from ultraviolet to far infrared, with a spectral resolution of 0.001 cm
1. The cell body was made from stainless steel in the form of a cylindrical tube with an inner diameter of 0.9 m and a length of 30 m. To investigate absorption spectra at elevated temperatures (up to 350 K) pipes for water circulation are mounted on the cylinder's outside surface and covered by thermo-insulating material. The temperature of the gas was measured by three equally spaced thermocouples along the cell. Pressure of the gas mixture was monitored by two capacitance manometers with full-scale ranges of 100-mbar (Baratron MKS) and 1050-mbar (Vacuubrand DVR-5). The cell is equipped with the White-type three mirror optical system. In order to increase the optical path length, a new set of mirrors with silver coatings was used. Parameters of the mirrors are much better than of those used earlier [7,11,12]. The reflection coefficient of the mirrors for the visible and infrared regions exceeded 0.98. Besides, the geometric sizes of the mirrors were increased: diameters of two back mirrors are 300 mm; the input front mirror is 500x300 mm in size. In the coupling system we used long-focus mirror, which reduced divergence of light beam outgoing from FTIR to diameters of 200 and 50 mm in the planes of back and front mirrors, respectively (see Fig. 1 in Ref. [7]). This allowed us to minimize the losses of light inside the cell and achieve the optical path length up to 1065.5 m. The tube and the mirrors assembled on individual supports. The supports of the mirrors are mounted on heavy concrete basements, which protect them against vibrations. Air tightness of the connection of mirrors supports with the tube is provided with bellows.

Thus the optical system is not affected by distortion of the shape of the tube due to temperature variations.

3. Application: investigation of selective and nonselective absorption spectra Weak selective and nonselective absorption spectra of CO2 and H2O in a wide spectral range [7,8,11–15] have been investigated since 2011 using the setup built. In this section we present new study of weak H2O spectral lines and a brief review of our previously obtained results. 3.1. Nonselective absorption of molecular gases Water vapor and carbon dioxide are the most important gases in the radiative balance of Earth, Venus and Mars. Besides the individual spectral lines, the spectra of these gases include nonselective or so-called continuum absorption which dominates in the transparency windows. Using FTIR spectrometer coupled with 30 m base length cell we investigated continuum absorption of water vapor in the absorption bands as well as in the transparency windows [7,8] and absorption of carbon dioxide beyond the band edges [15]. 3.1.1. Carbon dioxide Absorption spectra of CO2 were recorded within 6500– 9000 cm
1 spectral region with the optical path length of 836.5 m (see [15] and references therein). The measurements were carried out at the pressures of 396, 612, 801, 1004 mbar and the temperatures of 286, 286, 287, 288 K respectively. The CO2 absorption beyond the edges of 0 0 0 3 – 0 0 0 01, 1 0 0 32 – 0 0 0 01 and 1 0 0 31 – 0 0 0 01 bands was considered from the viewpoint of the asymptotic line wing shape theory under the assumption that the absorption is mainly determined by far wings of strong lines of adjacent bands of a monomer. The calculations produced the absorption coefficients close to experimental ones. 3.1.2. Water vapor The absorption spectra of water vapor were recorded within 800–4000 and 1800–10,000 cm
1 spectral regions with the optical path length of 612.26 m and spectral resolution of 0.03 cm
1. In the first spectral region the measurements were carried out at the pressures of 11.4, 19.4 mbar and at the temperatures of 288 and 318 K, respectively, in the second interval the pressure of 12.6 mbar and the temperature of 289.5 K were used [7]. Fig. 1 shows an example of the spectrum of retrieved continuum and its comparison with MT_CKD-2.5 [16] model and data reported by other teams [9,10,17–20]. The results we found agree well with the data obtained by other groups using FTIR spectrometers coupled with multipass cells [9,10,17]. Our further measurements of absorption spectra of water vapor with the optical path length increased to 1065.5 m confirm the previous results [8]. Nonetheless there are strong disagreements between these data and those obtained with the help of CRDS [18,19] and calorimetric measurements [20], especially in

Yu.N. Ponomarev et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 177 (2016) 253–260

Fig. 1. Absorption cross-sections of the water vapor self-continuum, derived at temperatures of 288 and 289.5 K [7] are shown in comparison with MT_CKD-2.5 [16] continuum model and the experimental data of Ptashnik et al. [10], Bicknell et al. [20], Mondelain et al. [18,19]. The lightgray and the dark-gray error-bars show the total error of the retrieved continuum in [10] and our study [7], respectively.

6200 cm
1 transparency window. Hence, new measurements are needed to determine the origins of these distinctions and derive correct values of continuum absorption. 3.2. Selective absorption spectra of molecular gases 3.2.1. Carbon dioxide The carbon dioxide spectra were investigated in the spectral region of 8790–11,505 cm
1 important for the studies of the Venus and Mars atmospheres [12,13]. The spectra were recorded with unapodized resolution 0.03 cm
1 at temperature 289 K using CO2 sample of 99.9% purity with natural isotopic abundance. The optical path length was equal to 726.7 m. The spectrometer was equipped with quartz beam splitter, Si detector and tungsten halogen lamp as a light source. The sensitivity (noise equivalent absorption) at the level of kν ¼7.2  10
10 cm
1 allowed the detection of numerous new transitions with the intensity values down to 5  10
29 cm/molecule (Fig. 2) [13]. The line positions and intensities of 16 CO2 vibrational bands were obtained. The line intensities of many weak vibrational bands of 12C16O2 and 16O12C18O were measured for the first time. The measured CO2 line intensities allowed determining the effective dipole moment parameters for corresponding transitions. 3.2.2. Water vapor An absorption spectrum of natural water vapor was recorded in the 2400 and 2560 cm
1 region at temperature of 12.5 C with the optical path length of 1065.5 m at a spectral resolution of 0.01 cm
1. This path length was gained with the use of a halogen lamp of 50 W as a light source, liquid nitrogen cooled InSb detector and the aperture diameter set at 1.5 mm. The water vapor pressure was 8.2 mbar. The signal-to-noise ratio (expressed as the maximum signal amplitude divided by the RMS noise amplitude) was calculated using the standard procedure of

255

Fig. 2. Spectrum of carbon dioxide recorded at 297 mbar near 9300 cm
1. The insert illustrates the noise level on the order of kind 7.2 10
10 cm
1 level [13].

the OPUS 6.5 software. The average value of the RMS noise amplitude in the spectral region under study was less than 10
4 and at the path length of 1065.5 m gave the minimal detectable absorption coefficient αmin ¼8.6  10
10 cm
1 (as it is illustrated in Fig. 3). This was achieved by coaddition of 2000 interferograms and using the spectral filters during the measurements. As a result, a large number of new weak water vapor absorption lines were observed. A Voigt profile was used for the lineshape retrieval and no particular signature has been observed on the fit residuals. The uncertainties of measured intensities for isolated lines were found to be 5–10% depending on their intensities. Calibration and assignment of the observed spectrum has been performed based on the empirical list constructed from the highly accurate experimental energy levels set derived in [21] and calculated intensities BT2 [22]. A very good agreement between the observed and empirical line positions has been obtained with an RMS deviation of 0.0006 cm
1 for 144 of 152 observed lines. The experimental line positions and intensities we obtained are presented in Table 1. In the assignment process the position and intensity matching between the observed transitions and empirical list were controlled. In total, 152 weak transitions could be assigned involving the rotational sublevels of the (010), (020), (100), and (001) upper vibrational states. More than a half of observed transitions originate from the (010) first excited vibrational state. As all assigned transitions involve the very well known upper and lower energy levels, then the most important experimental information concerned the measured line intensities. Comparison of the newly observed transitions with the most complete database of the published experimental transitions of water isotopologues [21] has shown that the intensity values of H216O lines in the region of interest have been previously measured at a room temperature by Toth [23–25] for 37 lines only. Seventeen more lines have been observed in [26–28], though no intensities values have been reported. In total, of 152 lines included in Table 1, 98 are newly observed. The average ratio and an RMS deviation between the presently

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Fig. 3. Water vapor spectrum in 2400–2560 cm
1 region. The sample pressure was 8.2 mbar. Three fragments illustrate the achieved absorption sensitivity in investigated spectral range.

reported and Toth intensities [23–25] were found to be 1.13% and 21%, respectively. Excluding four the worst outliers results in RMS 17% what is close to the experimental uncertainties 10–15% for measured intensities declared in [23–25]. The linelists generated from the empirically adjusted positions and accurate ab initio intensities (empirical lists) have been widely used in the HITRAN 2012 release for the H216O, H218O, and H217O isotopologues. The new edition of the GEISA database also includes large sets of the empirical transitions for H216O, H218O, H217O, and HD16O. While the accuracy of empirical line positions is obviously determined by the accuracy of the experimental energy levels used, the quality of the calculated variational intensities especially for the weak lines may be influenced in different ways and then needs additional checking. The effective procedure allowing discriminating the less accurate calculated intensities has been proposed in [29], it consists in comparison of four set of variational intensities obtained with two close, though different, potential energy and dipole moment surfaces. Those intensities which change much from one set to another are believed to be less accurate. No doubts, that this checking has to be combined with overall comparison of the calculated and measured intensities. Comparison of the observed intensities with BT2 [22] and recent improved variational calculations by Polyansky et al. [30] seems to be quite satisfactory with nearly equal RMS deviations of 22% and 19%, as it is illustrated in Fig. 4, where the intensity ratio with Toth experimental data [23– 25] is also included. The best agreement between the experiment and both calculations is achieved for the
26 largest measured intensities between 1  10 and
25 2  10 cm/mol. However, there is also a pattern of

distorted intensity ratio for both variational calculations between 2  10
26 and 3  10
26 cm/mol, which needs additional analysis. Ref. [30] intensities are more close to the measured values between 1  10
26 and 7  10
26 cm/ mol, where the BT2 data seem to be strongly underestimated for a number of transitions. Agreement between the newly observed intensities and those reported in the HITRAN 2012 DB [31] is also illustrated in Fig. 4, an RMS deviation for the intensity was estimated to be 35%. Detailed comparison of the observed intensities with all available calculated [22,30,32,33] and experimental [23–25] data is included in Table 1. Of 150 transitions in common with [31], 43 line intensities (marked by asterisk in Table 1) originate from Ref. [22], while 107 other data are taken from Ref. [32]. As it is seen from Fig. 4 and Table 1, transition intensities from HITRAN DB noticeably deviate from our data even for the strongest observed lines, where the comparison with both variational calculations [22,30] and experimental data [23–25] is quite satisfactory. This large discrepancy is caused by the inaccurate simulated on the base of the effective Hamiltonian approach intensities included in HITRAN from Ref. [32]. In fact, Ref. [32] combines both experimental and simulated data by Toth, still in HITRAN DB only simulated intensities [32] are chosen. It is interesting also to compare new measurements with the recent calculations of the water vapor transition intensities by Coudert et al. [33] performed within the effective Hamiltonian (EH) approach and included in the forthcoming GEISA 2015 release in 10–4700 cm
1 spectral region (12,500 transitions in total). Ratios between the experimental and EH [33] intensities are included in Fig. 5. As it is seen from the figure, the agreement between the experiment and EH simulation is much worse compared to

Yu.N. Ponomarev et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 177 (2016) 253–260

257

Table 1 Comparison of the presently measured transition intensities with the available experimental and calculated literature dataa. Wavenumber cm


1

2395.31860 2395.41271 2396.29994 2396.29994 2396.78769 2396.90974 2397.67687 2400.30627 2400.40078 2400.71778 2401.41125 2403.91852 2405.37193 2405.51573 2405.59262 2405.75531 2405.81597 2406.18315 2407.16579 2408.35775 2411.02910 2413.31524 2413.31524 2416.03846 2417.72602 2420.69465 2421.61916 2421.61916 2422.65823 2422.70806 2423.06877 2423.19243 2423.19243 2429.93256 2430.31651 2433.21780 2434.00819 2434.64500 2437.25573 2437.40099 2437.96495 2438.03945 2440.41933 2441.81584 2446.24025 2446.43106 2446.66378 2449.98101 2450.15492 2451.84212 2451.95982 2452.75326 2457.06701 2458.18139 2459.35949 2462.78041 2462.81596 2463.09704 2463.35615 2463.87720 2464.40567 2465.91133 2469.21073 2469.49555 2471.12185 2471.30988 2477.07721

Intensity

Intensity ratio

Upper b

cm/mol

[22]

[30]

[33]

HIT

6.90E-27 7.92E-27 8.69E-27 8.69E-27 4.58E-27 3.84E-26 8.01E-27 2.50E-26 1.94E-27 8.82E-27 2.83E-27 1.41E-26 4.30E-27 6.51E-26 2.33E-27 3.89E-27 1.67E-26 1.92E-26 1.87E-25 4.43E-27 2.02E-26 1.30E-27 1.30E-27 1.35E-26 2.94E-26 8.99E-27 4.26E-27 4.26E-27 3.71E-26 1.24E-25 2.16E-26 1.66E-27 1.66E-27 1.88E-25 2.58E-27 1.07E-26 3.96E-27 2.26E-26 9.86E-26 1.27E-25 1.55E-27 2.21E-26 5.85E-26 7.95E-27 4.76E-27 1.78E-27 3.68E-26 2.50E-27 1.36E-26 3.45E-27 4.18E-26 2.42E-27 5.44E-27 2.31E-26 1.26E-27 1.10E-26 1.01E-27 4.64E-26 2.16E-26 3.40E-26 3.30E-26 3.34E-26 8.74E-26 1.71E-27 5.31E-26 2.11E-26 9.93E-27

1.70 0.98 1.09 1.09 0.72 0.80 1.41 1.31 0.54 1.39 1.10 0.56 0.90 1.02 2.28 0.80 1.15 0.63 1.04 0.82 0.98 0.67 0.67 0.88 1.13 1.01 0.72 0.72 1.01 1.00 0.92 0.96 0.96 1.00 1.57 1.48 1.69 1.17 0.99 0.97 0.76 0.95 1.03 0.95 1.25 1.21 1.10 0.89 1.03 1.12 1.04 0.86 0.57 0.97 1.17 1.00 0.73 0.88 1.01 1.03 0.99 0.98 1.02 0.70 0.91 1.08 1.04

1.65 1.38 0.98 0.98 0.72 0.99 1.41 1.21 0.59 1.49 1.19 0.83 0.90 1.04 2.35 0.79 1.14 0.98 0.98 0.75 1.00 0.62 0.62 0.90 1.15 1.08 0.72 0.72 1.02 1.01 0.93 0.86 0.86 1.01 1.01 1.27 1.45 1.17 1.00 0.99 0.76 1.12 1.03 0.96 1.33 1.01 1.11 0.95 1.09 1.12 1.05 0.92 0.83 1.07 1.24 1.01 0.73 1.03 1.02 1.05 1.00 1.00 1.03 0.74 1.01 1.20 1.10

2.50 1.24 1.20 1.20 0.68 0.60 1.04 0.95 0.37 0.98 0.90 0.23 0.88 1.74

2.07 0.98n 1.82n 1.82 0.59 2.54 1.33 1.60 0.42 2.43 1.36 1.18 0.74 1.24 2.28n 0.87 1.16 1.09 1.05 1.03 1.21 0.67n 0.67n 0.76 1.10 1.24 0.72n 0.72n 1.18 1.12 0.73 0.96n 0.96n 1.09 1.57n 0.95 1.08 1.45 1.19 1.10 0.76n 2.39 1.10 0.75 1.65 1.21n 0.98 0.89n 1.39 0.75 1.13 0.71 0.62 1.81 1.17n 1.31 0.73n 3.17 0.80 1.35 1.11 1.16 1.07 0.71 1.06 1.24 1.24

0.88 1.26 0.99 1.06 0.58 1.75 0.58 0.58 0.82 1.06 0.58 0.82 0.82 1.44 1.30 0.90 1.30 1.15 4.42 0.57 0.65 1.84 1.57 1.18 0.59 0.72 1.06 0.86 0.70 1.35 0.99 3.03 0.68 1.11 1.09 0.39 0.26 0.76 0.53 2.65 0.39 0.93 0.89 2.77 1.30 1.42 0.95 0.31 0.46 0.54 0.55

c

Toth

0.75 1.08 1.19

0.62 0.97

1.09 1.26

1.45

2.01 1.21

0.98

1.22 1.11 0.85 1.25

1.07

0.85

0.99 1.18 1.03 0.96 1.08 0.96

δν

Lower

Ref.
1

VIB

J Ka Kc

VIB

J Ka Kc

cm

100 010 010 010 100 010 001 010 010 010 010 010 100 001 001 001 001 020 001 010 001 010 010 100 100 010 001 001 001 001 100 010 010 001 010 010 010 100 001 001 010 010 001 100 010 010 100 020 010 100 001 010 010 010 010 001 010 010 100 001 001 001 001 010 010 010 010

440 955 12120 12121 1156 863 1248 15312 1367 964 1257 972 1046 440 734 14114 14014 661 633 15412 441 14113 14114 735 744 872 15115 15015 541 533 936 13122 13121 624 1276 15213 15313 541 542 642 16512 964 734 826 973 1478 845 12112 1065 1147 743 1183 1174 761 1082 550 16413 1056 836 551 634 643 844 981 881 880 1074

010 000 000 000 010 000 010 000 000 000 000 000 010 010 010 010 010 010 010 000 010 000 000 010 010 000 010 010 010 010 010 000 000 010 000 000 000 010 010 010 000 000 010 010 000 000 010 000 000 010 010 000 000 000 000 010 000 000 010 010 010 010 010 000 000 000 000

313 808 11111 11110 1047 716 1147 14213 13112 919 12012 845 937 321 717 13113 13013 514 514 14113 322 13104 13103 606 615 827 14114 14014 422 414 827 12111 12112 505 1147 14114 14014 414 423 523 15213 817 615 717 928 1349 716 13211 10110 1038 624 1138 1047 616 1037 431 15114 909 707 432 515 524 725 936 752 753 1029

0.00402 0.00086 0.00203 0.00203 0.00054 0.00034 0.00135
0.00087
0.00099
0.00204 0.00257
0.00110 0.00275
0.00002
0.00059
0.00122 0.00135
0.00022
0.00006 0.00116
0.00002
0.00099
0.00244 0.00039 0.00032
0.00050
0.00005
0.00081
0.00036 0.00036 0.00018
0.00114
0.00115
0.00089 0.00075
0.00090 0.00025 0.00077 0.00028
0.00012 0.00026 0.00020
0.00008
0.00030
0.00122 0.00117 0.00014 0.00015
0.00073
0.00057
0.00036 0.00021
0.00009 0.00070 0.00022
0.00057 0.00020
0.00004 0.00038
0.00064 0.00006
0.00014 0.00005
0.00135
0.00041
0.00137 0.00005

new new [26] [26] [25] [23] [26] [23] new new new [23] new [24] new [26] [26] new [24] new [24] [26] [26] new [25] new [26] [26] [24] new [25] [26] [26] [24] new new new new [25] [24] new [23] [24] new new new [26] new new [27] [24] new new [23] new new new [23] new [25] [24] [24] [24] new [23] new new

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Table 1 (continued ) Wavenumber cm


1

2478.97744 2479.11278 2480.90629 2482.60988 2483.07880 2484.23329 2485.62542 2486.16861 2487.11825 2491.20397 2492.95418 2496.50452 2496.86413 2497.24929 2497.68886 2500.03229 2500.33038 2502.56817 2505.13434 2507.13818 2507.23020 2507.99027 2508.15683 2509.58860 2510.52019 2510.89637 2510.94951 2512.53647 2512.97726 2513.21554 2514.07792 2514.16889 2514.66300 2516.29299 2516.59002 2518.91917 2519.72210 2520.21078 2522.52764 2523.66773 2523.88548 2524.84093 2525.71078 2528.10827 2529.69291 2529.90300 2530.67992 2531.92683 2532.99809 2534.54961 2535.01742 2535.97601 2536.08863 2536.18455 2536.86473 2536.93622 2537.42727 2539.23411 2540.43727 2541.26870 2543.13222 2543.36498 2543.38750 2543.53479 2543.71307 2544.41919 2547.25729 2547.38447

Intensity

Intensity ratio

Upper b

cm/mol

[22]

[30]

[33]

HIT

3.15E-27 5.22E-27 4.81E-27 8.68E-26 4.63E-26 8.18E-28 6.73E-26 3.17E-26 1.45E-26 1.43E-26 1.32E-27 2.26E-26 3.74E-27 6.79E-26 7.72E-26 9.37E-27 1.44E-26 3.76E-28 2.74E-27 2.96E-27 1.12E-26 1.34E-26 4.71E-27 3.70E-27 6.84E-26 3.48E-27 4.17E-26 2.38E-27 2.71E-27 1.87E-27 2.20E-28 3.04E-26 1.28E-26 3.67E-27 1.23E-26 2.03E-27 4.88E-27 4.86E-26 1.68E-26 5.61E-28 2.85E-26 8.86E-28 6.45E-27 1.06E-27 6.53E-27 4.61E-27 1.54E-26 1.16E-26 1.66E-26 2.59E-27 4.25E-27 2.03E-26 9.87E-27 5.74E-28 8.17E-27 5.33E-28 9.49E-27 2.20E-26 1.13E-27 7.93E-27 8.33E-28 1.18E-27 4.10E-27 1.13E-27 1.56E-26 4.56E-26 2.93E-26 1.99E-28

1.29 1.04 1.07 1.00 1.02 0.87 0.92 1.01 0.96 1.00 1.15 0.93 1.13 0.91 0.99 1.01 1.04 0.72 1.16 0.99 1.02 1.02 1.08 0.98 0.99 0.74 1.02 1.26 0.93 0.95 1.70 1.00 0.95 0.72 1.00 0.78 1.01 0.92 0.91 1.20 0.99 0.92 1.04 0.90 1.00 0.90 1.00 0.99 1.05 1.35 1.04 1.21 1.04 0.77 1.06 1.23 0.97 1.15 1.02 0.88 1.05 0.89 1.03 1.00 0.98 1.00 0.96 0.72

1.38 1.03 1.08 1.00 1.03 0.86 1.05 1.02 0.98 1.01 1.17 1.03 1.12 1.02 1.00 1.02 1.05 0.72 1.23 1.06 1.08 1.04 1.10 1.03 1.01 0.94 1.04 1.25 0.94 1.01 1.77 1.02 1.03 0.84 1.02 1.01 1.02 1.03 1.01 1.26 1.07 0.97 1.05 0.93 1.00 0.92 1.02 1.00 1.06 1.36 1.04 1.34 1.06 0.81 1.06 1.58 0.98 1.28 1.08 0.99 1.06 0.91 1.05 1.00 1.06 1.01 1.08 0.73

0.96 1.87 0.94 1.01 2.01

1.38 1.36 0.88 1.09 1.28 0.87n 1.91 1.14 1.22 1.02 1.15n 1.04 1.40 1.04 1.16 0.71 1.26 0.72n 1.16n

0.70 1.25 1.99 0.85 0.46 1.42 0.45 1.33 0.87 1.56 0.71 0.61 2.25 5.05 5.34 2.08 1.37 0.83 1.71 1.21 0.78 0.48 1.18 0.72 0.95 0.80 0.41 0.88 0.45 0.45 0.62 0.61 0.38 0.99 2.40 2.73 3.09 1.00 1.33 4.81 1.18 1.47 0.31 0.87 0.94 0.78 0.88 2.14 0.43 0.80

0.60 1.39 0.47

1.02n 1.40 1.49 0.98n 1.15 0.96 1.27 1.26n 0.65 0.95n 1.70n 1.16 1.68 0.72n 0.97 0.34 0.75 0.94 0.94 1.46 0.92n 1.15 0.90n 1.43 1.21 1.35 0.99 1.23 1.35n 1.04n 2.60 1.27 0.77n 1.21 1.23n 1.04 1.94 1.02n 0.77 1.05n 0.89n 1.48 1.00n 1.48 1.17 0.84 0.72n

c

Toth

1.05

0.95

0.97 1.05 1.05

1.22 1.12

1.04

1.00

1.63

1.13

1.37

1.36

δν

Lower

Ref.
1

VIB

J Ka Kc

VIB

J Ka Kc

cm

010 100 100 001 001 020 010 001 001 001 001 010 100 010 001 100 001 100 010 010 020 001 001 020 001 010 001 100 100 010 001 001 010 010 100 010 100 010 010 010 010 010 001 001 100 001 001 001 001 100 020 010 001 010 001 010 001 010 020 010 100 001 001 020 010 001 010 100

1358 642 946 835 651 1029 1065 725 652 945 440 982 854 981 744 927 752 651 1166 771 11011 660 661 11111 735 1358 753 955 937 1175 845 853 862 1248 1056 1376 1047 1083 1082 770 872 881 954 541 743 761 762 936 845 752 818 1157 854 982 1046 1468 1055 1166 12111 1184 1157 770 771 928 973 826 1183 661

000 010 010 010 010 000 000 010 010 010 010 000 010 000 010 010 010 010 000 000 000 010 010 000 010 000 010 010 010 000 010 010 000 000 010 000 010 000 000 000 000 000 010 010 010 010 010 010 010 010 000 000 010 000 010 000 010 000 000 000 010 010 010 000 000 010 000 010

13013 515 817 716 532 1156 918 606 533 826 303 853 725 854 625 818 633 524 11111 624 12310 541 542 12210 616 12211 634 826 808 11210 808 734 717 11111 927 1249 918 954 955 707 725 836 835 404 616 642 643 817 726 625 945 10010 735 937 927 13311 936 1019 13410 1055 1028 651 652 1055 826 707 1056 532

0.00055 0.00011 0.00002 0.00011
0.00009 0.00040
0.00033 0.00003
0.00055
0.00021
0.00001
0.00001
0.00033 0.00020 0.00015
0.00028 0.00022 0.00047
0.00060 0.00033
0.00033
0.00087 0.00050
0.00077 0.00011 0.00038
0.00061 0.00045
0.00044
0.00036 0.00324 0.00018 0.00020 0.00013 0.00004
0.00029
0.00009 0.00014
0.00016 0.00002
0.00001
0.00095 0.00011 0.00041 0.00000 0.00095
0.00011
0.00005 0.00014
0.00066
0.00026
0.00087
0.00006
0.00031 0.00037 0.00128
0.00011
0.00012 0.00006
0.00023
0.00052
0.00058
0.00077
0.00005
0.00216 0.00007 0.00005 0.00255

new new new [24] new new [23] new new new new [23] new [23] [24] new new new new new [28] new new new [24] new [24] new new new new [24] new new [27] new new [23] new new [23] new new new new new [24] new new new new [23] new new [27] new new new new new new new new new new [24] new new

Yu.N. Ponomarev et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 177 (2016) 253–260

259

Table 1 (continued ) Wavenumber cm


1

2550.25330 2551.37984 2552.27285 2554.57260 2556.71093 2556.99998 2557.44767 2558.55068 2558.76049 2559.97720 2561.47843 2561.90617 2563.26506 2563.98220 2565.28295 2565.79134 2565.91578

Intensity

Intensity ratio

Upper b

cm/mol

[22]

[30]

[33]

HIT

1.18E-26 2.66E-27 1.28E-27 3.62E-27 1.82E-27 7.51E-27 1.27E-27 9.10E-27 5.62E-28 1.44E-26 9.44E-28 4.90E-28 1.59E-26 4.27E-27 1.35E-26 4.01E-27 1.55E-27

1.00 1.03 0.92 1.30 1.65 0.95 2.11 0.90 1.16 1.06 1.41 0.95 1.00 1.33 0.99 1.02 1.18

1.02 1.08 0.93 1.38 1.67 1.01 2.05 1.01 1.23 1.08 1.40 0.96 1.01 1.34 1.04 1.04 1.21

2.03 0.40 0.64 0.61 1.34 0.57

1.29 1.25 0.92n 1.25 1.65n 1.30 2.11n 0.59 1.16n 1.27 1.41n 0.95n 1.19 0.80 1.89 1.43 1.18n

0.43 1.61 0.82 1.21 1.06 1.63 5.50

c

Toth

1.78

δν

Lower

Ref.
1

VIB

J Ka Kc

VIB

J Ka Kc

cm

001 010 001 010 100 010 020 010 020 001 020 100 001 100 020 001 001

862 1083 1156 1276 1028 770 945 1285 13211 836 937 1148 955 1038 10010 871 872

010 000 010 000 010 000 000 000 000 010 000 010 010 010 000 010 010

743 1038 1037 12211 919 625 1074 1156 14510 717 1064 1019 836 909 1139 752 753


0.00020
0.00011 0.00012
0.00031
0.00112 0.00013
0.00218 0.00046
0.00052 0.00000
0.00024
0.00084 0.00014
0.00096
0.00063
0.00037
0.00009

new new new new new new new new new new new new [25] new [28] new new

a Intensity ratio is determined as Imeasured/Iliterature . δν – difference between the observed position and that evaluated from the experimental upper and lower energy levels [21]. Origin of the experimental literature data is given in the last column, where ‘new’ stands for newly observed line. b Ratio between presently measured intensities and those reported in HITRAN 2012 DB. c Comparison with the experimental data by Toth [23–25]. n Ratios with Ref. [22] data, other ratios concern comparison with Ref. [32].

H216O

Fig. 4. Ratio of the presently measured intensities to variational data from Refs. [22] (BT2) and [30] (Polyansky et al.), to HITRAN 2012 [31], and experimental values [23–25].

variational computations, with an RMS of 74% (!) for 136 compared lines. Large distortions up to 60–80% in intensity ratio are found even for the strongest observed lines.

4. Conclusion The FTIR spectrometer coupled with 30 m base length cell presented in the paper provides the optical path length more than 1 km long and allows us to achieve sensitivity 7.1  10
10 cm
1 and 8.6  10
10 cm
1 in spectral ranges near 9300 and 2500 cm
1, respectively.

Fig. 5. Ratio of the presently measured H216O intensities to calculated data obtained within the effective Hamiltonian approach in Ref. [33].

Brief review of our previous studies of weak lines and nonselective spectra of CO2 and H2O in a wide spectral region is presented. Much more attention was paid to new measurements of weak H216O lines between 2400 and
1 2560 cm . In this region about 150 weak absorption lines were recorded, 98 of them were observed for the first time. Measured line intensities were compared with the recent variational [22,30] and effective Hamiltonian [33] calculations, as well as with the data reported in HITRAN 2012 DB. It was concluded that our measurements even for the weakest lines are in a good consistency with variational data, and essentially disagree with the EH simulation [33]. Calculated intensities of Ref. [32] adopted in the HITRAN 2012 in the region of interest seem to be less

260

Yu.N. Ponomarev et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 177 (2016) 253–260

accurate compared to the new measurements with the RMS deviation of 35%. The further increase in the sensitivity at least by one order of magnitude in the visible and near IR ranges may be achieved by the use of LEDs. This work is in process. Acknowledgments

[15]

[16]

[17]

The work was supported by Programs of Fundamental Scientific Investigation I.10.3.7. (Project PhSI 01201354618) and II.10.3.8. (Project PhSI 01201354620).

[18]

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