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CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm−1
Journal of Quantitative Spectroscopy & Radiative Transfer 113 (2012) 2155–2166
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CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm 1 O. Leshchishina a, S. Mikhailenko b, D. Mondelain a, S. Kassi a, A. Campargue a,n a
Universite´ Grenoble 1/CNRS, UMR5588 LIPhy, Grenoble F-38041, France Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics, SB, Russian Academy of Science, 1, Akademician Zuev square, 634021 Tomsk, Russia
b
a r t i c l e i n f o
abstract
Article history: Received 30 May 2012 Received in revised form 27 June 2012 Accepted 29 June 2012 Available online 7 July 2012
The absorption spectrum of water vapor in ‘‘natural’’ isotopic abundance has been recorded by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) between 6885.79 and 7405.91 cm 1. This strong absorbing region includes the first hexad of interacting vibrational bands which was previously studied by Fourier Transform Spectroscopy. The achieved sensitivity of the recordings varies from amin 2 10–11 to 2 10 10 cm 1 allowing us to use a sample pressure of 0.1 Torr, making pressure broadening of the line profile mostly negligible. Weak lines in the vicinity of much stronger lines could then be accurately measured. The weakest lines have intensity on the order of 5 10–28 cm/molecule at 296 K. A set of 4471 lines were assigned to 4916 transitions of five water isotopologues (H216O, H218O, H217O, HD16O and HD18O). A small number of new energy levels was determined mostly for the H217O isotopologue. The previous investigations and existing databases are critically evaluated. In particular, a number of corrections and new assignments are proposed for the water list provided by the HITRAN database in the considered region. As a result, a complete list of 12,700 transitions for water in ‘‘natural’’ isotopic abundance is provided as Supplementary Material for the 6885–7408 cm 1 region. & 2012 Elsevier Ltd. All rights reserved.
Keywords: CRDS Water Vibration–rotation assignments H216O H218O H217O HD16O HITRAN
1. Introduction This paper extends the range of our investigations of the near infrared absorption spectrum of water vapor by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) (see Fig. 1). The present study covers the 6885.79–7405.91 cm 1 interval corresponding to a gap between our previous investigations of the H [1,2] and J [3] atmospheric transparency windows around 1.6 and 1.3 mm respectively. The 7050–7400 cm 1 region corresponds to very strong vibrational bands of the first hexad of interacting states {(040), (120), (021), (200), (101), (002)}. This region has been previously studied by Fourier
n Corresponding author. Tel.: þ33 4 76 51 43 19; fax: þ 33 4 76 63 54 95. E-mail address: [email protected] (A. Campargue).
0022-4073/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jqsrt.2012.06.026
transform spectroscopy (FTS) at pressures ranging from 1 to 15 Torr and path lengths from 1.5 up to 433 m [4–7]. These experimental conditions provided line parameters of strong and medium lines. The highest sensitivity of the CRDS technique combined with the use of samples at low pressure (about 0.1 Torr) allowed us extending significantly the set of observations. In particular, in the strongest absorption region around 7200 cm 1 the CRDS detection limit (2 10–27 cm/molecule at 296 K) lowers by about two orders of magnitude that of previous FTS measurements. This paper is organized as follows. Experimental aspects and line list construction are presented in the next Section 2. Section 3 includes the vibration–rotation assignments of the lines of the five water isotopologues (H216O, H218O, H217O, HD16O and HD18O) contributing to the CRDS spectrum as well as a comparison with previous studies. Section 4 presents a comparison of the measured
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2.2. Construction of the line list
Fig. 1. Overview of the H216O spectrum between 5800 and 8000 cm 1. The CRDS lists of Refs. [1–3] and of the present work are superimposed to the HITRAN line list [8].
line intensities with HITRAN database [8] and computed values [9] based on the results of Schwenke and Partridge (SP) calculations [10,11]. Critical evaluation of HITRAN database [8], comparison with experimental energy levels performed by an IUPAC task group for H218O, H217O and HD16O [12,13], and with a study of hot emission water spectrum [14] are given in Section 5.
The line centers and intensities were determined using an interactive least squares multi-line fitting program assuming a Voigt profile (http://sourceforge.net/projects/ fityk/ version v 0.8.6). The HWHM of the Gaussian component was fixed to the theoretical value of the Doppler width of H216O. Considering the low pressure of the recordings the pressure broadening was very limited. Nevertheless, as a consequence of the high sensitivity of the spectra, it was possible to adjust the Lorentzian component resulting of the small pressure broadening effects, at least for the strong and medium lines. The integrated line absorption coefficient, line position, Lorentzian widths and the corresponding local baseline (assumed to be a linear function of the wavenumber) were obtained from the multi-line fit. Fig. 2 illustrates the quality of the spectrum reproduction. In the displayed example, the (obs.-calc.) residuals reach the noise level (rms 3.2 10 11 cm 1). Note that none of the lines displayed on Fig. 2 is included in the HITRAN database. The line intensity, Sn0 (cm/molecule), of a rovibrational transition centered at n0, was obtained from the integrated
2. Experiment and data reduction 2.1. The CW-CRDS spectrometer The CW-CRDS spectrum of water at room temperature was recorded from 6885.79 to 7405.91 cm 1 with our fibered Distributed Feed-Back (DFB) diode laser CW-CRDS spectrometer. The reader may refer to Refs. [1,15,16] for a complete description of the experimental apparatus. The whole spectral region was continuously covered with the help of nineteen fibered DFB lasers. For each DFB laser, a tuning range of about 38 cm 1 was achieved by scanning the temperature from 10 to 60 1C while a constant current of 140 mA was maintained. The pair of high reflectivity mirrors (1 Ro58 ppm) of the ring down cell gives rise to ring down times between 80 and 330 ms depending on the wavenumber. About 30 ring down events were averaged for each spectral data point separated by about 2.7 10 3 cm 1 leading to a noise equivalent absorption ranging between 2 10 11 and 2 10 10 cm 1. A complete DFB temperature scan was achieved within 65 min. During the experiments, the pressure was continuously measured with a capacitance gauge (10 Torr, model 626B from MKS Instruments) as well as the ring down cell temperature (296.4 70.3 K). The spectra were recorded at pressures between 0.1 and 0.3 Torr. During each recording, the laser source wavenumber was monitored by a Fizeau type wavelength meter (WSU-30 HighFinesse, 5 MHz resolution and 20 MHz accuracy) giving an absolute calibration better than 1 10 3 cm 1 (30 MHz). The calibration was checked and refined using reference line positions of H2O from the HITRAN database [8]. We estimate to 1 10 3 cm 1 the uncertainty on the position of well isolated lines.
Fig. 2. Comparison of the CRDS spectrum of water recorded at 0.1 Torr with a simulation using a Voigt profile for each line. The (obs.–calc.) residuals displayed on the lower panel shows that the spectrum reproduction reaches the noise level (amin ¼ 3.2 10 11 cm 1). No lines are provided in the HITRAN database in the displayed region.
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absorption coefficient, An0 (cm 2): Z an dn ¼ Sn0 ðTÞN An0 ðTÞ ¼
ð1Þ
line
where n is the wavenumber in cm 1, an is the absorption coefficient in cm 1 obtained from the cavity ring down time, t (in s): a ¼ 1=ct1=ct0 where c is the light velocity and t0 is the ring-down time of the empty cavity and N is the molecular concentration in molecule/cm3 obtained from the measured pressure and temperature values: P¼NkT. The complete line list was obtained by gathering the lists corresponding to the different DFB laser diodes. 3. Line assignments and energy levels determination After removal of the lines due to CO2 present as impurity in the CRDS cell, a list of 4569 lines was obtained. The CRDS list is provided as Supplementary Material (Sup_Mat_1.txt). 4471 lines were assigned to 4916 transitions of five water
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isotopologues (H216O, H218O, H217O, HD16O and HD18O) leaving only 98 unassigned. Together with the experimental position and intensity values and corresponding rovibrational assignments, the SP values of the positions and intensities [10,11] are given for comparison. Note that the SP line intensities are given taking into account the isotopic abundance given in the HITRAN database and may deviate from the real abundance in our sample (see below). Except for a few H217O lines reaching new upper energy levels, all the other transitions involve previously determined experimental energy levels. Consequently, most of the line assignments (‘‘trivial’’ assignments) were performed by direct comparison of the CRDS line list to a list generated from experimental energy levels and calculated line intensities [9]. Table 1 presents the band by band comparison of the assigned transitions with those presented in the HITRAN database [8] in the same region. The current version of the HITRAN database includes 4300 transitions of four isotopologues (H216O, H218O, H217O and HD16O) in our region. According to the HITRAN
Table 1 Band by band statistics for the transitions assigned in the CRDS spectrum of water between 6885.79 and 7405.91 cm 1 and comparison to the HITRAN database. Band
This study
HITRAN
Number of transitions
J
Ka
Region/cm 1
Number of transitions
J
Ka
Region/cm 1
H216O 2n3 n1 þ 2n2 4n2 n1 þ n3 2n2 þ n3 2n1 þ n2 n2 3n2 þ n3 n2 2n1 n2 þ 2n3 n2 n1 þ n2 þ n3 n2 n1 þ 3n2 n2 5n2 6n2 n1 þ 2n2 þ n3 2n2
304 332 78 382 328 195 127 384 45 285 24 17 4 13
16 16 15 15 19 13 13 15 10 13 9 13 6 6
9 10 9 11 9 7 8 11 6 7 6 5 1 4
6885–7404 6886–7399 6886–7402 6886–7403 6887–7403 6888–7404 6889–7403 6890–7406 6895–7406 6900–7406 6919–7385 6928–7405 6937–7240 7059–7282
249 202 22 536 350 66 38 503 3 153 3 2 1
13 15 14 15 16 8 11 15 5 13 10 5 6
9 8 9 10 9 3 6 8 2 6 5 1 1
6889–7405 6886–7399 6886–7406 6891–7405 6885–7403 6900–7361 6889–7371 6890–7403 7044–7406 6932–7405 7009–7372 7195–7230 7008.05
H218O 2n1 2n2 þ n3 n1 þ 2n2 n1 þ n3 2n3 4n2 n1 þ n2 þ n3 n2 2n1 þ n2 n2
303 176 46 325 117 1 41 5
14 14 10 13 11 9 8 4
9 9 7 9 7 4 4 3
6886–7406 6887–7367 6888–7370 6889–7406 6922–7402 6999.48 7011–7327 7112–7259
274 129 18 355 64 1
12 12 7 13 8 9
7 6 5 7 5 4
6886–7400 6887–7358 6885–7138 6897–7406 6980–7405 6999.48
H217O n1 þ 2n2 2n2 þ n3 n1 þ n3 2n1 2n3 4n2 n1 þ n2 þ n3 n2
16 126 287 216 42 1 8
8 13 13 12 9 9 7
5 7 8 7 5 4 3
6887–7149 6887–7381 6887–7405 6889–7393 6991–7394 7013.7 7091–7319
12 106 305 240 33
5 12 12 11 6
4 6 7 7 3
6887–7056 6886–7381 6898–7405 6888–7393 7033–7405
HD16O 2n1 þ n2 2n3 n2 þ 2n3 n2
19 654 7
11 16 6
6 8 2
6886–7043 6907–7402 7103–7272
1 601
6 14
3 8
6912.26 6895–7403
HD18O 2n3
8
6
3
7151–7304
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reference indices, the corresponding positions and intensities were transferred from the line list constructed by R.A. Toth (http://mark4sun.jpl.nasa.gov/h2o.html). The graphical comparison of all previously observed transitions against those measured in this study is given on Fig. 3 for H216O, H218O, H217O and HD16O.
3.1. H216O lines The absorption spectrum of H216O in the 6885.8– 7405.9 cm 1 region has been studied in Refs. [1,2,4–7]. Among the 2518 CRDS observations of H216O transitions, 1224 are not included in the HITRAN database [8]. 178 additional observations were reported in Refs. [1,2,4–6]. Thus 1046 H216O transitions are newly observed (Fig. 3). For instance, transitions of the n1 þ2n2 þ n3 2n2 hot band are reported for the first time (see Table 1). In spite of the high number of newly detected transitions, no new H216O energy level was identified and all the derived values are found in good agreement with previous determinations (differences less than 0.003 cm 1).
3.2. H218O lines H218O transitions in the considered region were previously reported from ‘‘natural’’ water spectra [1,2] and from 18O-enriched water [17–20]. Among the 1014 CRDS observations of H218O transitions, 349 are not included in the HITRAN database [8]. 291 of them have been previously reported in Refs. [1,2,20] (Fig. 3). Thus, only 58 H218O transitions of six bands listed in Table 1 are observed for the first time. Compared to previous studies,
only one energy level was newly determined, namely (002) 100 10 at 8492.979 cm 1.
3.3. H217O lines In our region, H217O transitions were previously reported from ‘‘natural’’ water [1,2] and from 17O-enriched water [17,19]. Among the 696 CRDS observations of H217O transitions, 142 are not included in the HITRAN database [8]. 29 of them were reported in Refs. [2,19] leaving 113 newly observed transitions (Fig. 3). 15 new and 5 corrected energy levels of the (002), (021) and (200) vibrational states of H217O are listed in Table 2. The (002) 70 7 level was reported by Toth [19] with a term value of 7995.500 cm 1 but no transition reaching this level is provided in Ref. [19]. Our value of 7997.0527 cm 1 was obtained from the 2n3 70 7–81 8 transition at 7254.562 cm 1 in good agreement with the 7254.848 cm 1 value predicted by Schwenke and Partridge [10]. Our term value of the (021) 83 6 level (7902.3215 cm 1 instead of 7902.30785 cm 1 [19]) was determined from the 2n2 þ n3 83 6–73 5 transition at 7087.7109 cm 1. Toth derived his energy value using the same transition but with a different line position. In fact, the 7087.6971 cm 1 line of Ref. [19] is a superposition of two transitions with comparable intensities: 2n1 76 1–85 4 of H218O (7087.6904 cm 1, 17 1.45 10 26 cm/molecule) and 2n2 þ n3 83 6–73 5 of H2 O (7087.7109 cm 1, 1.20 10 26 cm/molecule). Toth assigned this blended line to H217O only, leading to an underestimated value for the (021) 83 6 level. Our value is confirmed by the 2n2 þ n3 83 6–93 7 transition at 6688.7612 cm 1 from Ref. [1] (7902.3240 cm 1) and by two transitions of the 2n2 þ n3 band: 83 6–95 5 at
Fig. 3. Comparison of the previous observations (blue triangles) to the present CRDS measurements (red dots) between 6885.79 and 7405.91 cm 1 for H216O, H218O, H217O and HD16O. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Table 2 New and corrected energy levels of H217O determined from the analysis of the CRDS spectrum of ‘‘natural’’ water vapor between 6885.79 and 7405.91 cm 1. VIB
J
Ka
Kc
Energy level (cm 1) This work
Previous studies
Ref.
7995.5000
[19]
7902.30785 7902.30769
[19] [12]
8111.74933 8111.74912 8150.73899 8150.73402
[19] [12] [19] [12]
8042.24036 8042.24251
[19] [12]
002 002
7 9
0 0
7 9
7997.0527 8319.6770
021 021 021
7 7 8
7 7 3
1 0 6
8425.8074 8425.8070 7902.3215
021 021 021
8 8 9
7 7 3
2 1 7
8620.7769 8620.7763 8111.7365
021
11
0
11
8150.7446
021 021
11 13
4 0
8 13
8764.3288 8614.5371
200
8
1
7
8042.0935
200 200 200 200 200 200 200 200
8 9 9 10 11 11 12 12
4 3 4 1 1 4 0 1
4 7 5 10 10 7 12 12
8280.3726 8362.6350 8502.6182 8264.2147 8658.4055 9024.8312 8689.3359 8689.3430
6432.0937 cm 1 and 83 6–93 7 at 6688.7603 cm 1 from Ref. [21] (7902.3197 and 7902.3231 cm 1, respectively). Our term value of the (021) 93 7 level is 8111.7365 cm 1 instead of 8111.74933 cm 1 [19]. We obtained this value from two transitions: 2n2 þ n3 93 7–10110 at 6999.6948 cm 1 and 2n2 þ n3 93 7–83 6 at 7107.9555 cm 1. Toth determined the (021) 93 7 level from one single line at 7107.968 cm 1 [19] which is in fact an unresolved doublet involving the 2n2 þ n3 93 7–83 6 transition and a ten times stronger H217O transition (2n1 31 3–40 4). Our value for the energy separation of the (021) 110 11 and (021) 111 11 levels (8.8 10 3 cm 1) differs from that of Ref. [19] (0.8 10 3 cm 1) while the same transitions were used to derive the energy levels. Our spectrum shows a well resolved doublet at 7038.6943 (2n2 þ n3 111 11–101 10) and 7038.7202 cm 1 (2n2 þ n3 110 11–100 10) which does not match the centers used by Toth [19] (7038.697 and 7038.714 cm 1). Toth [19] determined the term value of the (200) 81 7 level as 8042.24036 cm 1 from the 2n1 81 7–72 6 transition at 7334.224 cm 1. Fig. 4 shows that this transition is located about 0.147 cm 1 below at 7334.0771 cm 1 and that no absorption line is observed at 7334.224 cm 1. Our upper energy value of 8042.0935 cm 1 is confirmed by the observation of the 2n1 81 7–82 6 transition at 7060.5977 cm 1. 3.4. HD16O and HD18O lines Among the 680 CRDS observations of HD16O transitions, 187 are not included in the HITRAN database [8]. 127 of them were previously reported in Refs. [2,22,23].
Fig. 4. Comparison between the CRDS spectrum of water vapor at 0.1 Torr and a simulation based on the line list provided by the HITRAN database. An important shift is noted for the position of the 2n181 7–72 6 transition of H217O at 7334.224 cm 1. The observation of the 2n383 5–84 4 transition of H216O (marked by þ) which is missing in the HITRAN list [8] is an illustration of the interest of the low pressure recordings.
So, 60 HD16O transitions are newly detected (Fig. 3) but no new or corrected energy levels were determined. Eight HD18O transitions of the 2n3 band were assigned in the CRDS spectrum. These transitions were recently reported in Ref. [24] from an analysis of water spectrum enriched in deuterium and 18O. There is no spectral data for HD18O in the HITRAN database [8] in the considered range. Note that the relative ‘‘natural’’ abundance of HD18O in the CRDS sample is very small, about 6.23 10 7. 4. Line intensities A comparison of CRDS line intensities to Schwenke and Partridge (SP) calculated values [9] is presented in Fig. 5 for H216O, H218O, H217O and HD16O. The corresponding mean ratios are listed in Table 3. All the isotopologues included (about 3800 lines), the ICRDS/ISP mean intensity ratio is equal to 0.97 but significant deviations are noted for different isotopologues: 0.948 for H216O up to 1.045 for HD16O. The results of analogous comparisons of CRDS line intensities to HITRAN values [8] are shown in Fig. 6 and summarized in Table 3. The mean ICRDS/IHITRAN intensity ratio for more than 2500 lines is equal to 0.999 but as for the ICRDS/ISP ratios, the ICRDS/IHITRAN ratios vary from 0.959 for H218O up to 1.144 for HD16O. Figs. 5 and 6 show that, for the main isotopologue, the 5% underestimation of the CRDS intensities compared to HITRAN or SP values is constant over the wide 1 10 27– 1 10 22 cm/molecule intensity range. Considering the good agreement between the HITRAN and SP intensities (mean intensity ratio IHITRAN/ISP ¼1.019), we believe that
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Fig. 5. Ratio of the line intensities measured by CRDS between 6885.79 and 7405.91 cm 1 and the corresponding calculated values of Schwenke and Partridge for H216O, H218O, H217O and HD16O. The average ratios are indicated for each species. The CRDS intensity values do not include the 1.05 correction factor applied to the final values (see text).
Table 3 Ratios of CRDS intensities by the calculated values of Schwenke and Partridge (SP) and by HITRAN values. Molecule CRDS/SP
H216O H218O H217O HD16O Total
CRDS/HITRAN
Number of lines
Mean ratioa
Number of lines
Mean ratioa
1990 813 517 461 3781
0.948/0.995 0.981/1.030 0.967/1.015 1.045/1.097 0.970/1.019
1133 569 436 380 2518
0.966/1.014 0.959/1.007 0.997/1.047 1.144/1.201 0.999/1.049
a The second value is the first one multiplied by a factor 1.05 in order to correct a probable 5% error on the measured pressure value of the CRDS recordings (see text).
an error on the order of 5% on the pressure values of the CRDS recordings is probably responsible of the observed systematic shift. Such an error is acceptable considering that we used a pressure gauge with a 10 Torr full range to measure pressure values on the order of 0.1 Torr. Consequently, experimental intensity values included in the lists attached as Supplementary Material are the experimental values multiplied by a factor of 1.05. Our spectra were recorded at different pressures between 0.1
and 0.3 Torr and in principle, the correction should be pressure dependent (an error on the zero pressure has a three times larger impact on the 0.1 Torr recordings than on the 0.3 Torr recordings) but we believe that the adopted 5% correction improves significantly our intensity values in an effective way. The resulting uncertainty is expected to be less than 5%. The corrected average intensity values included in Table 3 indicate a small isotopic enrichment for the minor isotopologues which is possible considering that prior to the present measurements, the same CRDS cell was filled with different 18O and deuterium enriched species. It is worth mentioning that we are using the SP variational line lists while more recent calculated lists are now available (see for instance Refs. [25,26]). In fact, while in the high energy range above 15,000 cm 1, recent calculations represent a significant improvement over SP lists, in our region, new variational line lists are mostly identical to SP lists (at least for non deuterated species). Consequently, the above comparisons hold independently of the used variational list. In particular, a small number of strong transitions were measured by CRDS by Lisak et al. in our region, achieving experimental uncertainties at the 0.5% level [27] (these very strong transitions are saturated in our spectrum). Similar good agreement (at the 1% level) is obtained with SP intensity values and the BT2 line list of Ref. [26].
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2161
Fig. 6. Ratio of the line intensities measured by CRDS between 6885.79 and 7405.91 cm 1 and the corresponding HITRAN values for H216O, H218O, H217O and HD16O. The average ratios are indicated for each species. The CRDS intensity values do not include the 1.05 correction factor applied to the final values (see text).
5. Comparison to the HITRAN and IUPAC databases and emission spectra 5.1. HITRAN database Among the 4300 water transitions provided by the HITRAN database [8] in the studied region, 33 are listed without assignment. 1910 CRDS transitions are not included in the HITRAN database. On the other hand, a total of 1264 HITRAN transitions are absent from the CRDS list: (i) 847 strong transitions with intensities between 2.9 10 24 and 1.8 10 20 cm/molecule are not included in the CRDS line list due to line saturation effects (ii) 402 additional transitions are absent in the CRDS list (intensities between 1.8 10 27 and 5.9 10 24 cm/molecule) because they were either calculated and measured from isotopically enriched spectra or are overlapped or blended with much stronger lines in the spectrum of ‘‘natural’’ water. The present analysis allowed us to assign most of the lines left unassigned in the HITRAN line list. The results are given in Table 4. Two of them (7040.7720, 1.32 10 26 and 7386.9183, 1.01 10 25) are not water lines. While the 33 unassigned lines are all labeled as H216O, eight of them are in fact due to H218O, H217O, or HD16O (see Table 4 and the file Sup_Mat_2.txt provided as Supplementary Materials). Furthermore, we found that 81 lines of the HITRAN list have erroneous parameters (position, intensity, isotopologue or vibration–rotation assignment) (see Table 5). At least six of them are not water lines. For 26 transitions included in Table 5, the HITRAN positions differ from the real positions by more than 0.2 cm 1 (up to 12.66 cm 1).
52 transitions have erroneous intensity values with IHITRAN/ISP ratio ranging between 2.6 and 6.5 105 (see Sup_Mat_2.txt). For instance, Fig. 7 shows two examples of lines with correct positions but with intensity overestimated by several orders of magnitude. 5.2. IUPAC database When available, the experimental energy levels of H218O, H217O and HD16O published by an IUPAC task group [12,13] were used for a comparison to the CRDS observations. The line positions corresponding to the CRDS measurements were calculated using the sets of energy levels available on the web site http://chaos.chem. elte.hu/marvel/. All three sets are dated June 3, 2010. 17 Except for three H218O and 48 H2 O transitions, all CRDS 18 17 line positions of H2 O, H2 O and HD16O could be calculated from the IUPAC energy levels. The average differences are (in 10 3 cm 1 unit): 0.43, 0.15 and 0.05 17 for 1011 H218O, 646 H2 O and 680 HD16O lines, respectively. Excluding evident outliers, the three corresponding rms values are about 1.8 10 3 cm 1. An overview comparison of the deviations for the three considered isotopologues is shown on Fig. 8. About 65% of the CRDS positions are in very good agreement with the IUPAC line positions (9nCRDS–nIUPAC9r0.001 cm 1). The largest differences for the H218O and HD16O line positions are within 0.01 cm 1 while the differences for the H217O line positions range from 0.014 to þ0.013 cm 1. As expected from the above discussion (see Section 3.3 and Fig. 4), the (nCRDS–nIUPAC) difference for the transitions reaching the (200) 81 7 upper level is about 0.15 cm 1.
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Table 4 Assignments of the lines of water left unassigned in the HITRAN list between 6885.79 and 7405.91 cm 1. HITRAN Pos. (cm 1)
Int.a
6906.3313 6911.8468 6912.0708 6940.1090 6942.6810 6959.1580 6969.9314 6989.3075 6995.1886 6995.3935
2.57E-26 2.53E-26 1.07E-25 1.41E-25 6.78E-26 1.86E-25 2.59E-26 8.88E-26 7.67E-26 2.42E-26
7040.7720 7069.5463 7083.0064 7130.3284
1.32E-26 1.21E-25 3.37E-26 1.02E-26
7177.5405 7200.4790 7224.7620 7247.4463 7257.7924 7258.8775 7265.9314 7275.3433 7278.6838 7279.2866 7293.3759
4.96E-26 2.42E-26 8.27E-26 9.76E-26 1.05E-25 1.21E-26 1.02E-25 1.08E-25 3.23E-25 5.65E-26 3.05E-25
7315.2919 7360.6218 7360.8162 7371.5639 7386.9183 7392.8410 7397.2415 7401.5442
1.82E-25 1.61E-25 1.61E-25 4.03E-25 1.01E-25 1.74E-25 3.91E-25 9.08E-26
Exp. pos.b (cm 1) 6906.3279 6911.8503 6912.0678 6940.1080 6942.6829 6959.1639 6969.9340 6989.3073 6995.1889 6995.3944 6995.3950 Not water 7069.5474 7083.0081 7130.3111 7130.3078 7177.5419 7200.4760 7224.7640 7247.4474 7257.7936 7258.8788 7265.9409 7275.3478 7278.6834 7279.2861 7293.3772 7293.3796 7315.2931 7360.6208 7360.8151 7371.5630 Not water 7392.8409 7397.2394 7401.5495
SP Int.c
Elow (cm 1)d
ISOe
Rovibrational assignment
2.48E-26 1.69E-26 6.66E-26 1.63E-25 6.33E-26 1.91E-25 2.61E-26 8.31E-26 7.39E-26 1.59E-26 5.31E-27
1551.2051 2327.9143 1437.9689 141.9024 1080.3856 1327.1102 1557.8451 1985.7855 1695.0691 3109.9121 3109.9121
H218O
200 120 120 021 040 120 200 200 120 031 031
11 0 11 000 12 0 12 13 3 10 000 14 2 13 10 3 7 000 10 2 8 4 1 4 000 3 1 3 9 5 5 000 9 2 8 12 1 12 000 11 0 11 13 1 13 000 12 0 12 11 4 8 000 11 5 7 14 4 8 000 11 3 9 7 7 0 010 7 7 1 7 7 1 010 7 7 0
5.00E-26 3.57E-26 4.45E-27 4.09E-27 6.02E-26 4.15E-26 5.81E-26 8.55E-26 1.01E-25 1.44E-26 1.03E-25 1.88E-25 3.78E-25 4.98E-26 1.72E-25 5.72E-26 1.86E-25 1.65E-25 5.49E-26 4.20E-25
2572.1395 2211.1908 1611.6532 1141.6915 1437.9689 1774.6168 1198.1999 2300.6853 2271.7125 1574.4497 583.7778 1960.2077 1985.7855 2251.8628 2254.2843 2254.2844 2054.3691 1907.6160 1907.4518 647.0720
031 210 101 002 120 200 200 200 210 200 002 200 200 210 200 200 021 210 210 021
8 4 4 010 7 4 3 6 1 5 010 6 2 4 10 4 7 000 10 4 6 11 1 10 000 12 2 9 10 5 5 000 10 2 8 11 4 8 000 12 1 11 9 3 6 000 9 2 7 12 6 6 000 12 5 7 6 4 3 010 6 3 4 10 5 6 000 10 4 7 6 1 6 000 7 0 7 12 3 9 000 12 2 10 11 6 6 000 11 5 7 5 5 0 010 5 4 1 10 9 2 000 10 8 3 10 9 1 000 10 8 2 11 7 4 000 10 7 3 4 4 1 010 3 3 0 4 4 0 010 3 3 1 7 5 3 000 6 3 4
1.63E-25 4.23E-25 6.35E-26
601.9608 1293.0186 2129.5994
H217O
H218O 16
HD O
H218O
H218O H218O
H217O H217O
002 7 1 7 000 6 2 4 120 11 4 8 000 10 1 9 210 5 5 0 010 4 4 1
a
Line intensity (cm 1/ molecule cm 2 at 296 K) from HITRAN database [1]. Line position (cm 1) calculated from experimental energy levels. c SP calculated line intensity (cm 1/ molecule cm 2 at 296 K) [9,11]. d Experimental value (cm 1) of the lower energy level. e Isotopologue, if not H216O. b
It is difficult to analyze systematically the origin of the large values of the 9nCRDS–nIUPAC9 differences. Part of them is due to the lack of precision of the energy level determination when it relies from a single transition. For instance, the IUPAC term value of the (200) 93 7 level 17 of H2 O relies on a single transition reported in Ref. [19] and is shifted by about 0.013 cm 1 from our value (see Section 3.3 and Table 2). In the same time, there are situations when the IUPAC task group used several transitions from different experimental sources but obtained inaccurate energy levels. As an example, we consider the (021) 83 6 level of H217O obtained by Toth [19] from a single transition corresponding to a blended line. As mentioned in Section 3.3, our value is 0.014 cm 1 higher than Toth’s value. The value recommended by the IUPAC task group [12] was obtained from three transitions reported in Refs. [1,19,21] but they were weighted according to different precision values: 0.001 cm 1 for Ref. [19] and 0.010 cm 1 for Refs. [1,21]. As a result, the
IUPAC energy level value is mainly determined by the line position of Ref. [19] which is actually inaccurate. Consequently, the line positions of Ref. [21] reaching the (021) 83 6 level (2n2 þ n3 83 6–95 5 and 2n2 þ n3 83 6–93 7) deviate by 0.0114 and 0.0145 cm 1, respectively while they were both used for the determination of the IUPAC energy level. The difference between the CRDS and IUPAC line positions of the 2n2 þ n3 83 6–73 5 is also about 0.014 cm 1 confirming that the IUPAC weighting is incorrect. 5.3. Comparison to emission spectra The emission spectrum of water vapor has been studied in our region by Zobov et al. [14]. The line list of Ref. [14] contains more than 4100 H216O transitions between 6885 and 7406 cm 1. We compared 1094 positions reported by Zobov et al. [14] to the absorption measurements of Refs. [4–7] and of the present study. The differences range between 0.08 and þ0.08 cm 1. The average difference
O. Leshchishina et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 113 (2012) 2155–2166
2163
Table 5 Corrections of position, intensity or rovibrational assignments of 81 transitions of the HITRAN list between 6885.79 and 7405.91 cm 1. HITRAN Pos. (1)
Our assignment Int. (2)
Assignment (3)
Exp. Pos. (4)
SP Int. (5)
6928.7453 6935.9826 6955.1750 6964.0592 6976.6451 6985.8910 7008.3642 7014.8352 7028.7531 7064.5059 7073.4298 7075.8118 7091.4224 7131.8923 7132.4493 7135.5490 7141.7914 7143.5322
2.05E-26 1.17E-25 2.42E-25 8.47E-26 3.23E-26 9.60E-26 5.33E-25 5.69E-26 7.67E-25 2.12E-26 6.05E-26 1.61E-25 4.44E-25 9.08E-25 5.49E-26 8.07E-25 9.12E-26 5.24E-25
002 111 120 120 200 120 200 002 200 031 040 101 111 101 120 200 101 021
11 5 7 000 12 6 7 6 1 010 8 6 9 3 7 000 9 2 12 1 12 000 11 0 11 4 8 000 11 5 15 0 15 000 14 1 7 1 7 000 6 4 7 3 5 000 7 6 9 4 6 000 9 5 6 5 2 010 5 5 5 5 1 000 4 0 5 0 5 000 4 4 7 3 4 010 6 5 9 1 9 000 8 3 9 6 3 000 10 3 8 1 8 000 7 2 13 6 7 000 13 6 13 1 12 000 12 1
6 2 8 11 7 14 2 2 5 1 4 0 1 6 8 5 8 11
6918.3619 6935.9624 6958.8835 6959.1639 6989.3073 6985.9849 7008.3643 7014.8347 7028.7528 7064.0700 7073.4286 7075.8115 7091.4291 7131.8927 7132.4489 7135.5492 7146.4318 7144.0325
1.09E-26 1.93E-27 9.43E-26 1.91E-25 8.31E-26 7.09E-27 2.10E-29 1.82E-27 2.26E-26 1.28E-26 4.55E-28 6.26E-27 2.67E-27 2.06E-26 3.18E-27 2.23E-26 1.29E-26 5.37E-25
7143.7130 7153.5367 7172.3062 7185.5770 7194.4825 7196.6953 7223.6495 7224.8419 7259.7206 7266.2356 7266.2368 7276.6492 7280.0156 7305.2434 7318.6601 7352.3253 7370.5604 7375.1013 7388.6202 7404.9363 7405.7177
2.06E-26 4.44E-26 1.41E-25 1.13E-23 4.48E-25 1.61E-25 4.03E-26 3.19E-26 5.37E-26 4.03E-24 4.03E-25 6.05E-26 4.84E-25 4.03E-25 2.02E-25 2.02E-26 7.71E-26 1.98E-24 5.12E-26 1.91E-25 2.73E-25
021 210 120 200 200 021 002 002 210 101 002 200 120 101 210 021 031 012 021 111 012
97 42 11 4 61 12 3 13 3 11 5 11 6 51 93 31 12 3 94 93 82 96 85 20 87 11 6 52
3 000 10 5 6 3 010 3 3 0 7 000 12 1 12 6 000 5 2 3 9 000 13 2 12 11 000 12 3 10 7 000 11 6 6 5 000 12 5 8 5 010 4 0 4 6 000 9 3 7 3 000 4 2 2 9 000 12 2 10 6 000 9 1 9 7 000 10 1 10 7 010 7 1 6 4 000 10 2 9 3 010 7 3 4 2 010 2 1 1 1 000 8 5 4 6 010 11 4 7 4 010 4 3 1
7143.7126 7153.5374 7173.5698 7185.5771 7193.1810 7196.6934 7213.2662 7224.8431 7259.7259 7266.2357 7266.2369 7275.3478 7280.0156 7305.2436 7318.6583 7352.3256 7370.5575 7375.1014 7388.6204 7404.9364 7405.7204
2.35E-27 6.53E-27 7.34E-27 2.26E-24 1.22E-26 6.52E-25 7.02E-27 6.25E-28 1.88E-25 7.95E-26 3.66E-24 1.88E-25 8.62E-26 1.42E-25 5.91E-26 5.12E-29 2.93E-26 6.35E-27 5.86E-29 o 1.00E-30 1.40E-28
H218O 6906.4694
2.31E-26
200 11 0 11 000 12 1 12
6906.3279
2.48E-26
6957.7789 6960.0437 7026.4115
3.37E-26 2.21E-26 4.92E-26
101 7 3 5 000 7 5 2 021 9 4 6 000 10 2 9 101 7 1 6 000 6 5 1
6957.7795 6960.0439 7026.4126
4.57E-27 7.05E-27 1.00E-28
7069.5805 7074.7307 7074.8370 7103.5223 7110.0282 7111.8231 7128.9058 7146.8163
1.46E-26 2.02E-25 2.42E-26 1.74E-25 6.05E-26 9.32E-27 1.48E-26 1.34E-26
002 021 002 021 002 101 101 200
6 8 7 4 6 6 7 7
1 3 3 4 2 3 3 1
6 6 5 0 5 4 5 7
000 000 000 000 000 000 000 000
7 7 8 4 7 5 6 6
2 3 4 2 3 5 5 2
5 5 4 3 4 1 2 4
7069.2660 7074.7307 7074.8369 7103.5232 7110.0290 7111.8236 7128.9063 7146.8175
1.56E-26 5.95E-26 5.77E-27 1.27E-27 1.34E-26 1.42E-28 8.37E-29 1.38E-28
7169.4121 7175.7246 7204.8401 7266.2555 7279.3803 7281.9030 7293.8720
2.30E-26 6.90E-26 2.88E-26 9.88E-26 2.06E-25 7.42E-25 6.25E-25
200 002 002 002 002 200 200
6 7 2 6 7 7 8
1 2 0 1 3 2 2
6 5 2 6 5 6 7
000 000 000 000 000 000 000
5 8 3 7 7 7 8
2 3 3 0 4 1 1
3 6 1 7 4 7 8
7169.4127 7175.7308 7204.8404 7265.9409 7279.3802 7281.9031 7293.8721
3.09E-27 9.58E-27 1.01E-28 1.03E-25 5.79E-27 7.37E-26 1.03E-25
Exp. Pos. (6)
SP Int. (7)
ISO (8)
Assignment (9)
H216O Not water Not water Not water 6964.0627 6976.6485 6985.8918
8.85E-26 3.48E-27 9.913E-26
7064.5122
3.34E-26
120 12 0 12 000 11 1 11 210 6 4 3 010 6 5 2 040 12 3 10 000 11 0 11
031 6 5 1 010 5 5 0 18
7075.8160 7091.4344
1.26E-25 4.39E-25
H2 O
7141.7871 7143.5308 7143.5384
1.46E-25 3.71E-25 1.97E-25
002 10 2 8 000 11 3 9 002 11 1 10 000 12 2 11 002 8 2 6 000 8 5 3
7172.3072
1.27E-25
021 15 2 14 000 14 2 13
101 8 1 7 000 8 3 6 021 15 1 15 000 14 1 14
Not water 7223.6468
4.37E-26
040 14 5 10 000 13 2 11
7276.6406
5.03E-26
120 8 4 5 000 7 1 6
7352.3150
1.57E-26
7375.1012
1.98E-24
002 4 0 4 000 3 3 1
7405.7229
1.51E-25
200 13 3 11 000 12 2 10
6906.4583 6906.4780
8.34E-27 7.40E-27
200 11 1 11 000 12 0 12 101 10 4 7 000 11 4 8
7026.4174 7026.4178
4.64E-26 1.55E-26
021 7 7 1 000 7 7 0 021 7 7 0 000 7 7 1
7074.7411
1.51E-25
Not water H216O 210 5 0 5 010 5 1 4
7103.5245
1.83E-25
H216O
120 9 6 4 000 9 5 5
7111.8197
3.69E-27
17 H2 O
200 6 5 1 000 7 4 4
7146.8130 7146.8155 7146.8185
2.83-27 9.43E-28 8.16-27
7266.2566 7279.3823
1.37E-25 1.52E-25
HD16O H216O
002 2 0 2 000 1 1 1 021 13 5 9 000 12 5 8
7293.8663 7293.8692
8.87E-24 4.52E-25
H216O H216O
002 8 3 6 000 8 4 5 021 10 7 4 000 9 7 3
HD16O
002 10 5 5 000 9 5 4
002 11 0 11 000 12 1 12 002 11 1 11 000 12 0 12 111 1 1 1 010 2 1 2
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Table 5 (continued ) HITRAN Pos. (1)
Our assignment Int. (2)
Assignment (3)
Exp. Pos. (4)
SP Int. (5)
7303.5059 7308.2219 7338.0350 7347.8724 7357.7665 7404.8748
2.20E-26 4.84E-26 7.42E-26 5.77E-26 3.93E-26 3.06E-26
021 021 200 200 200 002
8 3 6 000 7 1 7 5 5 1 000 4 3 2 4 3 2 000 3 2 1 11 0 11 000 10 1 10 12 1 12 000 11 0 11 6 1 6 000 5 2 3
7303.5059 7308.2219 7338.0352 7347.7307 7357.4541 7404.5602
1.53E-27 1.76E-27 8.18E-28 6.33E-26 2.44E-26 2.61E-26
H217O 6908.4716 6977.1542 6989.7377 7013.3049 7136.0347 7215.8081 7277.5076 7278.1270 7322.7163 7344.9030 7366.2690
1.36E-26 8.07E-27 2.00E-26 4.32E-26 8.71E-27 5.04E-27 3.00E-25 1.81E-26 4.52E-26 3.61E-26 9.76E-26
200 101 021 002 200 002 200 200 200 200 101
80 11 1 75 20 62 61 80 10 1 66 80 11 1
8 000 10 000 3 000 2 000 5 000 6 000 8 000 10 000 0 000 8 000 10 000
HD16O 6912.2569 7196.6979 7260.2314 7301.1096 7311.4705 7353.0972
6.41E-26 1.17E-25 2.02E-25 2.39E-26 1.99E-25 3.09E-25
210 002 002 002 002 002
63 95 62 43 52 14 2
4 5 4 2 4 12
9 1 11 3 65 33 6 1 70 71 90 73 9 1 11 3
9 9 2 1 6 7 7 9 5 9 9
6908.4735 6977.0874 6989.8554 7013.4406 7134.5576 7215.8072 7277.5084 7277.9879 7322.8339 7346.1128 7366.2690
4.41E-27 4.64E-28 2.16E-26 3.65E-28 1.04E-26 1.49E-29 7.81E-26 1.92E-26 4.71E-26 3.19E-26 2.23E-30
000 5 2 000 9 5 000 6 2 000 5 1 000 5 0 000 14 1
3 4 5 5 5 13
6912.2570 7196.6979 7260.2314 7301.1098 7311.4704 7353.0974
1.20E-27 1.19E-26 6.45E-26 3.66E-32 2.22E-26 4.52E-28
Exp. Pos. (6)
SP Int. (7)
ISO (8)
Assignment (9)
7293.8798
1.36E-24
H216O
021 10 7 3 000 9 7 2
7347.8736 7357.7619 7404.8742
2.15E-26 1.19E-28 1.29E-26
H216O H216O
200 11 1 11 000 10 0 10 002 13 4 9 000 14 3 12 050 13 0 13 000 12 3 10
Not water 7013.3059 7136.0354
4.44E-26 6.41E-26
H216O
002 7 1 7 000 8 2 6 002 5 2 3 000 5 5 0
7277.5167
1.21E-25
H218O
200 2 2 0 000 1 1 1
Notations: (1), (2), and (3) are line position (cm 1), line intensity (cm 1/ molecule cm 2 at 296 K), and vibration–rotation assignment of the upper and lower levels from HITRAN database [8]. (4)—line position (cm 1) calculated from experimental energy levels of the transition given in column (3). (5)—SP calculated line intensity (cm 1/ molecule cm 2 at 296 K) of the transition given in column (3). (6)—line position (cm 1) calculated from experimental energy levels of the transition given in column (9). (7)—SP calculated line intensity (cm 1/ molecule cm 2 at 296 K) of the transition given in column (9). (8)—isotopologue if different from HITRAN. (9)—our vibration–rotation assignment.
Fig. 7. Comparison of the CRDS spectrum of water vapor recorded at 0.1 Torr to the corresponding simulation using the HITRAN line list showing two examples of ‘‘phantom’’ lines (markedn) included in the HITRAN database [8] but absent in the CRDS spectrum. In fact, the position of the two problematic lines is correct but their HITRAN intensity is overestimated by several orders of magnitude (see Table 5).
O. Leshchishina et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 113 (2012) 2155–2166
2165
Fig. 9. Upper panel: CRDS (this work) and HITRAN line lists for water between 6885 and 7408 cm 1. Lower panel: Corresponding ‘‘complete’’ line list calculated from the experimentally determined energy levels combined to variational intensities (intensity cut off of 1 10 28 cm/molecule at 296 K).
Fig. 8. Histograms of the differences between the CRDS line positions of H218O, H217O, and HD16O and those calculated by using the IUPAC energy levels [12,13].
is 0.0017 cm 1 and the rms value is 0.0158 cm 1. Using all available H216O experimental energy levels, 2158 line positions can be calculated and compared to those of Ref. [14]. The differences range from -0.29 to þ0.37 cm 1 in this case and the room mean square deviation is 0.0208 cm 1. This rms value agrees with the average uncertainty claimed in Ref. [14] for the spectra obtained with a torch at atmospheric pressure. It confirms that as a result of the line broadening and blends (and then multiple assignments for many lines), hot spectra can hardly be used for accurate determination of energy levels. 5.4. A ‘‘complete’’ line list for water in the 6885–7408 cm 1 region In order to provide the most complete line list in the region, a list of 12,700 transitions for water in ‘‘natural’’ isotopic abundance is given as Supplementary Material (Sup_Mat_3.txt file). The intensity cut off was fixed to 1 10 28 cm/molecule. Most of the line positions were calculated from the experimental values of the energy levels and associated intensities at 296 K are the variational values [9]. Above the chosen intensity cut off, 525
weak transitions reach upper energy levels which are not yet experimentally determined. In those situations, we reproduced SP line positions. The corresponding line positions (marked SP) may deviate significantly (up to 0.3 cm 1) from their real values. Some of these SP line positions could be corrected on the basis of the general tendency of the (obs.–calc.) deviations of the series of upper energy levels (the corresponding transitions are marked ‘‘estimation’’). Fig. 9 shows an overview of the ‘‘complete’’ line list compared to the HITRAN and CRDS lists. 6. Conclusion The spectroscopic parameters of more than 4900 water transitions were measured by CRDS between 6885 and 7408 cm 1. As a result of the sensitivity of the CRDS recordings and of the use of low pressure values (typically 0.1 Torr) about 1300 medium and weak lines could be newly detected. The minimum intensity values are on the order of 5 10 28 cm/molecule i.e. between one and two orders of magnitude lower than the HITRAN intensity cut off for H216O in the investigated region. The gain is particularly important for the major isotopologue and the H217O species. The rovibrational analysis was performed by using the previously obtained experimental energy levels as well as calculated spectra of different water species. Finally, 21 new and corrected energy levels belonging to four vibrational states of H217O and H218O were determined from the vibration–rotation analysis. The analysis led to new or corrected assignments for more than one hundred lines included in the HITRAN database [8] (see Tables 4, 5 and Sup_Mat_2.txt file).
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A few inaccuracies in the energy sets of the IUPAC task group [12] were evidenced and corrected. Nevertheless, the critical review and validation of the energy levels performed by the IUPAC task group for H217O, H218O, HD16O, HD17O, and HD18O [12,13] represent a considerable improvement compared to the present status of the HITRAN database, both in terms of completeness and accuracy. A major result of the present work is the construction of a ‘‘complete’’ list of 12,700 transitions for water in ‘‘natural’’ abundance between 6885 and 7408 cm 1 (intensity cut off of 1 10 28 cm 1/ molecule cm 2 at 296 K).
[8]
[9] [10]
[11]
[12]
Acknowledgments [13]
This work is jointly supported by CNRS (France) and RFBR (Russia) in the in the frame of Groupement de Recherche International SAMIA (Spectroscopie d’Absorption des Mole´cules d’Inte´rˆet Atmosphe´rique), as well as by RFBR-CNRS Grant no. 10-05-93105. The work of S.M. was also partly supported by the program 3.9.6 of the Russian Academy of Sciences (RAS) and by the program 22 ‘‘Fundamental problems of the Solar system studies’’ of the Presidium RAS. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j. jqsrt.2012.06.026.
[14]
[15]
[16]
[17] [18]
[19] [20]
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CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm 1 O. Leshchishina a, S. Mikhailenko b, D. Mondelain a, S. Kassi a, A. Campargue a,n a
Universite´ Grenoble 1/CNRS, UMR5588 LIPhy, Grenoble F-38041, France Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics, SB, Russian Academy of Science, 1, Akademician Zuev square, 634021 Tomsk, Russia
b
a r t i c l e i n f o
abstract
Article history: Received 30 May 2012 Received in revised form 27 June 2012 Accepted 29 June 2012 Available online 7 July 2012
The absorption spectrum of water vapor in ‘‘natural’’ isotopic abundance has been recorded by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) between 6885.79 and 7405.91 cm 1. This strong absorbing region includes the first hexad of interacting vibrational bands which was previously studied by Fourier Transform Spectroscopy. The achieved sensitivity of the recordings varies from amin 2 10–11 to 2 10 10 cm 1 allowing us to use a sample pressure of 0.1 Torr, making pressure broadening of the line profile mostly negligible. Weak lines in the vicinity of much stronger lines could then be accurately measured. The weakest lines have intensity on the order of 5 10–28 cm/molecule at 296 K. A set of 4471 lines were assigned to 4916 transitions of five water isotopologues (H216O, H218O, H217O, HD16O and HD18O). A small number of new energy levels was determined mostly for the H217O isotopologue. The previous investigations and existing databases are critically evaluated. In particular, a number of corrections and new assignments are proposed for the water list provided by the HITRAN database in the considered region. As a result, a complete list of 12,700 transitions for water in ‘‘natural’’ isotopic abundance is provided as Supplementary Material for the 6885–7408 cm 1 region. & 2012 Elsevier Ltd. All rights reserved.
Keywords: CRDS Water Vibration–rotation assignments H216O H218O H217O HD16O HITRAN
1. Introduction This paper extends the range of our investigations of the near infrared absorption spectrum of water vapor by high sensitivity CW-Cavity Ring Down Spectroscopy (CW-CRDS) (see Fig. 1). The present study covers the 6885.79–7405.91 cm 1 interval corresponding to a gap between our previous investigations of the H [1,2] and J [3] atmospheric transparency windows around 1.6 and 1.3 mm respectively. The 7050–7400 cm 1 region corresponds to very strong vibrational bands of the first hexad of interacting states {(040), (120), (021), (200), (101), (002)}. This region has been previously studied by Fourier
n Corresponding author. Tel.: þ33 4 76 51 43 19; fax: þ 33 4 76 63 54 95. E-mail address: [email protected] (A. Campargue).
0022-4073/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jqsrt.2012.06.026
transform spectroscopy (FTS) at pressures ranging from 1 to 15 Torr and path lengths from 1.5 up to 433 m [4–7]. These experimental conditions provided line parameters of strong and medium lines. The highest sensitivity of the CRDS technique combined with the use of samples at low pressure (about 0.1 Torr) allowed us extending significantly the set of observations. In particular, in the strongest absorption region around 7200 cm 1 the CRDS detection limit (2 10–27 cm/molecule at 296 K) lowers by about two orders of magnitude that of previous FTS measurements. This paper is organized as follows. Experimental aspects and line list construction are presented in the next Section 2. Section 3 includes the vibration–rotation assignments of the lines of the five water isotopologues (H216O, H218O, H217O, HD16O and HD18O) contributing to the CRDS spectrum as well as a comparison with previous studies. Section 4 presents a comparison of the measured
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2.2. Construction of the line list
Fig. 1. Overview of the H216O spectrum between 5800 and 8000 cm 1. The CRDS lists of Refs. [1–3] and of the present work are superimposed to the HITRAN line list [8].
line intensities with HITRAN database [8] and computed values [9] based on the results of Schwenke and Partridge (SP) calculations [10,11]. Critical evaluation of HITRAN database [8], comparison with experimental energy levels performed by an IUPAC task group for H218O, H217O and HD16O [12,13], and with a study of hot emission water spectrum [14] are given in Section 5.
The line centers and intensities were determined using an interactive least squares multi-line fitting program assuming a Voigt profile (http://sourceforge.net/projects/ fityk/ version v 0.8.6). The HWHM of the Gaussian component was fixed to the theoretical value of the Doppler width of H216O. Considering the low pressure of the recordings the pressure broadening was very limited. Nevertheless, as a consequence of the high sensitivity of the spectra, it was possible to adjust the Lorentzian component resulting of the small pressure broadening effects, at least for the strong and medium lines. The integrated line absorption coefficient, line position, Lorentzian widths and the corresponding local baseline (assumed to be a linear function of the wavenumber) were obtained from the multi-line fit. Fig. 2 illustrates the quality of the spectrum reproduction. In the displayed example, the (obs.-calc.) residuals reach the noise level (rms 3.2 10 11 cm 1). Note that none of the lines displayed on Fig. 2 is included in the HITRAN database. The line intensity, Sn0 (cm/molecule), of a rovibrational transition centered at n0, was obtained from the integrated
2. Experiment and data reduction 2.1. The CW-CRDS spectrometer The CW-CRDS spectrum of water at room temperature was recorded from 6885.79 to 7405.91 cm 1 with our fibered Distributed Feed-Back (DFB) diode laser CW-CRDS spectrometer. The reader may refer to Refs. [1,15,16] for a complete description of the experimental apparatus. The whole spectral region was continuously covered with the help of nineteen fibered DFB lasers. For each DFB laser, a tuning range of about 38 cm 1 was achieved by scanning the temperature from 10 to 60 1C while a constant current of 140 mA was maintained. The pair of high reflectivity mirrors (1 Ro58 ppm) of the ring down cell gives rise to ring down times between 80 and 330 ms depending on the wavenumber. About 30 ring down events were averaged for each spectral data point separated by about 2.7 10 3 cm 1 leading to a noise equivalent absorption ranging between 2 10 11 and 2 10 10 cm 1. A complete DFB temperature scan was achieved within 65 min. During the experiments, the pressure was continuously measured with a capacitance gauge (10 Torr, model 626B from MKS Instruments) as well as the ring down cell temperature (296.4 70.3 K). The spectra were recorded at pressures between 0.1 and 0.3 Torr. During each recording, the laser source wavenumber was monitored by a Fizeau type wavelength meter (WSU-30 HighFinesse, 5 MHz resolution and 20 MHz accuracy) giving an absolute calibration better than 1 10 3 cm 1 (30 MHz). The calibration was checked and refined using reference line positions of H2O from the HITRAN database [8]. We estimate to 1 10 3 cm 1 the uncertainty on the position of well isolated lines.
Fig. 2. Comparison of the CRDS spectrum of water recorded at 0.1 Torr with a simulation using a Voigt profile for each line. The (obs.–calc.) residuals displayed on the lower panel shows that the spectrum reproduction reaches the noise level (amin ¼ 3.2 10 11 cm 1). No lines are provided in the HITRAN database in the displayed region.
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absorption coefficient, An0 (cm 2): Z an dn ¼ Sn0 ðTÞN An0 ðTÞ ¼
ð1Þ
line
where n is the wavenumber in cm 1, an is the absorption coefficient in cm 1 obtained from the cavity ring down time, t (in s): a ¼ 1=ct1=ct0 where c is the light velocity and t0 is the ring-down time of the empty cavity and N is the molecular concentration in molecule/cm3 obtained from the measured pressure and temperature values: P¼NkT. The complete line list was obtained by gathering the lists corresponding to the different DFB laser diodes. 3. Line assignments and energy levels determination After removal of the lines due to CO2 present as impurity in the CRDS cell, a list of 4569 lines was obtained. The CRDS list is provided as Supplementary Material (Sup_Mat_1.txt). 4471 lines were assigned to 4916 transitions of five water
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isotopologues (H216O, H218O, H217O, HD16O and HD18O) leaving only 98 unassigned. Together with the experimental position and intensity values and corresponding rovibrational assignments, the SP values of the positions and intensities [10,11] are given for comparison. Note that the SP line intensities are given taking into account the isotopic abundance given in the HITRAN database and may deviate from the real abundance in our sample (see below). Except for a few H217O lines reaching new upper energy levels, all the other transitions involve previously determined experimental energy levels. Consequently, most of the line assignments (‘‘trivial’’ assignments) were performed by direct comparison of the CRDS line list to a list generated from experimental energy levels and calculated line intensities [9]. Table 1 presents the band by band comparison of the assigned transitions with those presented in the HITRAN database [8] in the same region. The current version of the HITRAN database includes 4300 transitions of four isotopologues (H216O, H218O, H217O and HD16O) in our region. According to the HITRAN
Table 1 Band by band statistics for the transitions assigned in the CRDS spectrum of water between 6885.79 and 7405.91 cm 1 and comparison to the HITRAN database. Band
This study
HITRAN
Number of transitions
J
Ka
Region/cm 1
Number of transitions
J
Ka
Region/cm 1
H216O 2n3 n1 þ 2n2 4n2 n1 þ n3 2n2 þ n3 2n1 þ n2 n2 3n2 þ n3 n2 2n1 n2 þ 2n3 n2 n1 þ n2 þ n3 n2 n1 þ 3n2 n2 5n2 6n2 n1 þ 2n2 þ n3 2n2
304 332 78 382 328 195 127 384 45 285 24 17 4 13
16 16 15 15 19 13 13 15 10 13 9 13 6 6
9 10 9 11 9 7 8 11 6 7 6 5 1 4
6885–7404 6886–7399 6886–7402 6886–7403 6887–7403 6888–7404 6889–7403 6890–7406 6895–7406 6900–7406 6919–7385 6928–7405 6937–7240 7059–7282
249 202 22 536 350 66 38 503 3 153 3 2 1
13 15 14 15 16 8 11 15 5 13 10 5 6
9 8 9 10 9 3 6 8 2 6 5 1 1
6889–7405 6886–7399 6886–7406 6891–7405 6885–7403 6900–7361 6889–7371 6890–7403 7044–7406 6932–7405 7009–7372 7195–7230 7008.05
H218O 2n1 2n2 þ n3 n1 þ 2n2 n1 þ n3 2n3 4n2 n1 þ n2 þ n3 n2 2n1 þ n2 n2
303 176 46 325 117 1 41 5
14 14 10 13 11 9 8 4
9 9 7 9 7 4 4 3
6886–7406 6887–7367 6888–7370 6889–7406 6922–7402 6999.48 7011–7327 7112–7259
274 129 18 355 64 1
12 12 7 13 8 9
7 6 5 7 5 4
6886–7400 6887–7358 6885–7138 6897–7406 6980–7405 6999.48
H217O n1 þ 2n2 2n2 þ n3 n1 þ n3 2n1 2n3 4n2 n1 þ n2 þ n3 n2
16 126 287 216 42 1 8
8 13 13 12 9 9 7
5 7 8 7 5 4 3
6887–7149 6887–7381 6887–7405 6889–7393 6991–7394 7013.7 7091–7319
12 106 305 240 33
5 12 12 11 6
4 6 7 7 3
6887–7056 6886–7381 6898–7405 6888–7393 7033–7405
HD16O 2n1 þ n2 2n3 n2 þ 2n3 n2
19 654 7
11 16 6
6 8 2
6886–7043 6907–7402 7103–7272
1 601
6 14
3 8
6912.26 6895–7403
HD18O 2n3
8
6
3
7151–7304
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reference indices, the corresponding positions and intensities were transferred from the line list constructed by R.A. Toth (http://mark4sun.jpl.nasa.gov/h2o.html). The graphical comparison of all previously observed transitions against those measured in this study is given on Fig. 3 for H216O, H218O, H217O and HD16O.
3.1. H216O lines The absorption spectrum of H216O in the 6885.8– 7405.9 cm 1 region has been studied in Refs. [1,2,4–7]. Among the 2518 CRDS observations of H216O transitions, 1224 are not included in the HITRAN database [8]. 178 additional observations were reported in Refs. [1,2,4–6]. Thus 1046 H216O transitions are newly observed (Fig. 3). For instance, transitions of the n1 þ2n2 þ n3 2n2 hot band are reported for the first time (see Table 1). In spite of the high number of newly detected transitions, no new H216O energy level was identified and all the derived values are found in good agreement with previous determinations (differences less than 0.003 cm 1).
3.2. H218O lines H218O transitions in the considered region were previously reported from ‘‘natural’’ water spectra [1,2] and from 18O-enriched water [17–20]. Among the 1014 CRDS observations of H218O transitions, 349 are not included in the HITRAN database [8]. 291 of them have been previously reported in Refs. [1,2,20] (Fig. 3). Thus, only 58 H218O transitions of six bands listed in Table 1 are observed for the first time. Compared to previous studies,
only one energy level was newly determined, namely (002) 100 10 at 8492.979 cm 1.
3.3. H217O lines In our region, H217O transitions were previously reported from ‘‘natural’’ water [1,2] and from 17O-enriched water [17,19]. Among the 696 CRDS observations of H217O transitions, 142 are not included in the HITRAN database [8]. 29 of them were reported in Refs. [2,19] leaving 113 newly observed transitions (Fig. 3). 15 new and 5 corrected energy levels of the (002), (021) and (200) vibrational states of H217O are listed in Table 2. The (002) 70 7 level was reported by Toth [19] with a term value of 7995.500 cm 1 but no transition reaching this level is provided in Ref. [19]. Our value of 7997.0527 cm 1 was obtained from the 2n3 70 7–81 8 transition at 7254.562 cm 1 in good agreement with the 7254.848 cm 1 value predicted by Schwenke and Partridge [10]. Our term value of the (021) 83 6 level (7902.3215 cm 1 instead of 7902.30785 cm 1 [19]) was determined from the 2n2 þ n3 83 6–73 5 transition at 7087.7109 cm 1. Toth derived his energy value using the same transition but with a different line position. In fact, the 7087.6971 cm 1 line of Ref. [19] is a superposition of two transitions with comparable intensities: 2n1 76 1–85 4 of H218O (7087.6904 cm 1, 17 1.45 10 26 cm/molecule) and 2n2 þ n3 83 6–73 5 of H2 O (7087.7109 cm 1, 1.20 10 26 cm/molecule). Toth assigned this blended line to H217O only, leading to an underestimated value for the (021) 83 6 level. Our value is confirmed by the 2n2 þ n3 83 6–93 7 transition at 6688.7612 cm 1 from Ref. [1] (7902.3240 cm 1) and by two transitions of the 2n2 þ n3 band: 83 6–95 5 at
Fig. 3. Comparison of the previous observations (blue triangles) to the present CRDS measurements (red dots) between 6885.79 and 7405.91 cm 1 for H216O, H218O, H217O and HD16O. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Table 2 New and corrected energy levels of H217O determined from the analysis of the CRDS spectrum of ‘‘natural’’ water vapor between 6885.79 and 7405.91 cm 1. VIB
J
Ka
Kc
Energy level (cm 1) This work
Previous studies
Ref.
7995.5000
[19]
7902.30785 7902.30769
[19] [12]
8111.74933 8111.74912 8150.73899 8150.73402
[19] [12] [19] [12]
8042.24036 8042.24251
[19] [12]
002 002
7 9
0 0
7 9
7997.0527 8319.6770
021 021 021
7 7 8
7 7 3
1 0 6
8425.8074 8425.8070 7902.3215
021 021 021
8 8 9
7 7 3
2 1 7
8620.7769 8620.7763 8111.7365
021
11
0
11
8150.7446
021 021
11 13
4 0
8 13
8764.3288 8614.5371
200
8
1
7
8042.0935
200 200 200 200 200 200 200 200
8 9 9 10 11 11 12 12
4 3 4 1 1 4 0 1
4 7 5 10 10 7 12 12
8280.3726 8362.6350 8502.6182 8264.2147 8658.4055 9024.8312 8689.3359 8689.3430
6432.0937 cm 1 and 83 6–93 7 at 6688.7603 cm 1 from Ref. [21] (7902.3197 and 7902.3231 cm 1, respectively). Our term value of the (021) 93 7 level is 8111.7365 cm 1 instead of 8111.74933 cm 1 [19]. We obtained this value from two transitions: 2n2 þ n3 93 7–10110 at 6999.6948 cm 1 and 2n2 þ n3 93 7–83 6 at 7107.9555 cm 1. Toth determined the (021) 93 7 level from one single line at 7107.968 cm 1 [19] which is in fact an unresolved doublet involving the 2n2 þ n3 93 7–83 6 transition and a ten times stronger H217O transition (2n1 31 3–40 4). Our value for the energy separation of the (021) 110 11 and (021) 111 11 levels (8.8 10 3 cm 1) differs from that of Ref. [19] (0.8 10 3 cm 1) while the same transitions were used to derive the energy levels. Our spectrum shows a well resolved doublet at 7038.6943 (2n2 þ n3 111 11–101 10) and 7038.7202 cm 1 (2n2 þ n3 110 11–100 10) which does not match the centers used by Toth [19] (7038.697 and 7038.714 cm 1). Toth [19] determined the term value of the (200) 81 7 level as 8042.24036 cm 1 from the 2n1 81 7–72 6 transition at 7334.224 cm 1. Fig. 4 shows that this transition is located about 0.147 cm 1 below at 7334.0771 cm 1 and that no absorption line is observed at 7334.224 cm 1. Our upper energy value of 8042.0935 cm 1 is confirmed by the observation of the 2n1 81 7–82 6 transition at 7060.5977 cm 1. 3.4. HD16O and HD18O lines Among the 680 CRDS observations of HD16O transitions, 187 are not included in the HITRAN database [8]. 127 of them were previously reported in Refs. [2,22,23].
Fig. 4. Comparison between the CRDS spectrum of water vapor at 0.1 Torr and a simulation based on the line list provided by the HITRAN database. An important shift is noted for the position of the 2n181 7–72 6 transition of H217O at 7334.224 cm 1. The observation of the 2n383 5–84 4 transition of H216O (marked by þ) which is missing in the HITRAN list [8] is an illustration of the interest of the low pressure recordings.
So, 60 HD16O transitions are newly detected (Fig. 3) but no new or corrected energy levels were determined. Eight HD18O transitions of the 2n3 band were assigned in the CRDS spectrum. These transitions were recently reported in Ref. [24] from an analysis of water spectrum enriched in deuterium and 18O. There is no spectral data for HD18O in the HITRAN database [8] in the considered range. Note that the relative ‘‘natural’’ abundance of HD18O in the CRDS sample is very small, about 6.23 10 7. 4. Line intensities A comparison of CRDS line intensities to Schwenke and Partridge (SP) calculated values [9] is presented in Fig. 5 for H216O, H218O, H217O and HD16O. The corresponding mean ratios are listed in Table 3. All the isotopologues included (about 3800 lines), the ICRDS/ISP mean intensity ratio is equal to 0.97 but significant deviations are noted for different isotopologues: 0.948 for H216O up to 1.045 for HD16O. The results of analogous comparisons of CRDS line intensities to HITRAN values [8] are shown in Fig. 6 and summarized in Table 3. The mean ICRDS/IHITRAN intensity ratio for more than 2500 lines is equal to 0.999 but as for the ICRDS/ISP ratios, the ICRDS/IHITRAN ratios vary from 0.959 for H218O up to 1.144 for HD16O. Figs. 5 and 6 show that, for the main isotopologue, the 5% underestimation of the CRDS intensities compared to HITRAN or SP values is constant over the wide 1 10 27– 1 10 22 cm/molecule intensity range. Considering the good agreement between the HITRAN and SP intensities (mean intensity ratio IHITRAN/ISP ¼1.019), we believe that
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Fig. 5. Ratio of the line intensities measured by CRDS between 6885.79 and 7405.91 cm 1 and the corresponding calculated values of Schwenke and Partridge for H216O, H218O, H217O and HD16O. The average ratios are indicated for each species. The CRDS intensity values do not include the 1.05 correction factor applied to the final values (see text).
Table 3 Ratios of CRDS intensities by the calculated values of Schwenke and Partridge (SP) and by HITRAN values. Molecule CRDS/SP
H216O H218O H217O HD16O Total
CRDS/HITRAN
Number of lines
Mean ratioa
Number of lines
Mean ratioa
1990 813 517 461 3781
0.948/0.995 0.981/1.030 0.967/1.015 1.045/1.097 0.970/1.019
1133 569 436 380 2518
0.966/1.014 0.959/1.007 0.997/1.047 1.144/1.201 0.999/1.049
a The second value is the first one multiplied by a factor 1.05 in order to correct a probable 5% error on the measured pressure value of the CRDS recordings (see text).
an error on the order of 5% on the pressure values of the CRDS recordings is probably responsible of the observed systematic shift. Such an error is acceptable considering that we used a pressure gauge with a 10 Torr full range to measure pressure values on the order of 0.1 Torr. Consequently, experimental intensity values included in the lists attached as Supplementary Material are the experimental values multiplied by a factor of 1.05. Our spectra were recorded at different pressures between 0.1
and 0.3 Torr and in principle, the correction should be pressure dependent (an error on the zero pressure has a three times larger impact on the 0.1 Torr recordings than on the 0.3 Torr recordings) but we believe that the adopted 5% correction improves significantly our intensity values in an effective way. The resulting uncertainty is expected to be less than 5%. The corrected average intensity values included in Table 3 indicate a small isotopic enrichment for the minor isotopologues which is possible considering that prior to the present measurements, the same CRDS cell was filled with different 18O and deuterium enriched species. It is worth mentioning that we are using the SP variational line lists while more recent calculated lists are now available (see for instance Refs. [25,26]). In fact, while in the high energy range above 15,000 cm 1, recent calculations represent a significant improvement over SP lists, in our region, new variational line lists are mostly identical to SP lists (at least for non deuterated species). Consequently, the above comparisons hold independently of the used variational list. In particular, a small number of strong transitions were measured by CRDS by Lisak et al. in our region, achieving experimental uncertainties at the 0.5% level [27] (these very strong transitions are saturated in our spectrum). Similar good agreement (at the 1% level) is obtained with SP intensity values and the BT2 line list of Ref. [26].
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2161
Fig. 6. Ratio of the line intensities measured by CRDS between 6885.79 and 7405.91 cm 1 and the corresponding HITRAN values for H216O, H218O, H217O and HD16O. The average ratios are indicated for each species. The CRDS intensity values do not include the 1.05 correction factor applied to the final values (see text).
5. Comparison to the HITRAN and IUPAC databases and emission spectra 5.1. HITRAN database Among the 4300 water transitions provided by the HITRAN database [8] in the studied region, 33 are listed without assignment. 1910 CRDS transitions are not included in the HITRAN database. On the other hand, a total of 1264 HITRAN transitions are absent from the CRDS list: (i) 847 strong transitions with intensities between 2.9 10 24 and 1.8 10 20 cm/molecule are not included in the CRDS line list due to line saturation effects (ii) 402 additional transitions are absent in the CRDS list (intensities between 1.8 10 27 and 5.9 10 24 cm/molecule) because they were either calculated and measured from isotopically enriched spectra or are overlapped or blended with much stronger lines in the spectrum of ‘‘natural’’ water. The present analysis allowed us to assign most of the lines left unassigned in the HITRAN line list. The results are given in Table 4. Two of them (7040.7720, 1.32 10 26 and 7386.9183, 1.01 10 25) are not water lines. While the 33 unassigned lines are all labeled as H216O, eight of them are in fact due to H218O, H217O, or HD16O (see Table 4 and the file Sup_Mat_2.txt provided as Supplementary Materials). Furthermore, we found that 81 lines of the HITRAN list have erroneous parameters (position, intensity, isotopologue or vibration–rotation assignment) (see Table 5). At least six of them are not water lines. For 26 transitions included in Table 5, the HITRAN positions differ from the real positions by more than 0.2 cm 1 (up to 12.66 cm 1).
52 transitions have erroneous intensity values with IHITRAN/ISP ratio ranging between 2.6 and 6.5 105 (see Sup_Mat_2.txt). For instance, Fig. 7 shows two examples of lines with correct positions but with intensity overestimated by several orders of magnitude. 5.2. IUPAC database When available, the experimental energy levels of H218O, H217O and HD16O published by an IUPAC task group [12,13] were used for a comparison to the CRDS observations. The line positions corresponding to the CRDS measurements were calculated using the sets of energy levels available on the web site http://chaos.chem. elte.hu/marvel/. All three sets are dated June 3, 2010. 17 Except for three H218O and 48 H2 O transitions, all CRDS 18 17 line positions of H2 O, H2 O and HD16O could be calculated from the IUPAC energy levels. The average differences are (in 10 3 cm 1 unit): 0.43, 0.15 and 0.05 17 for 1011 H218O, 646 H2 O and 680 HD16O lines, respectively. Excluding evident outliers, the three corresponding rms values are about 1.8 10 3 cm 1. An overview comparison of the deviations for the three considered isotopologues is shown on Fig. 8. About 65% of the CRDS positions are in very good agreement with the IUPAC line positions (9nCRDS–nIUPAC9r0.001 cm 1). The largest differences for the H218O and HD16O line positions are within 0.01 cm 1 while the differences for the H217O line positions range from 0.014 to þ0.013 cm 1. As expected from the above discussion (see Section 3.3 and Fig. 4), the (nCRDS–nIUPAC) difference for the transitions reaching the (200) 81 7 upper level is about 0.15 cm 1.
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Table 4 Assignments of the lines of water left unassigned in the HITRAN list between 6885.79 and 7405.91 cm 1. HITRAN Pos. (cm 1)
Int.a
6906.3313 6911.8468 6912.0708 6940.1090 6942.6810 6959.1580 6969.9314 6989.3075 6995.1886 6995.3935
2.57E-26 2.53E-26 1.07E-25 1.41E-25 6.78E-26 1.86E-25 2.59E-26 8.88E-26 7.67E-26 2.42E-26
7040.7720 7069.5463 7083.0064 7130.3284
1.32E-26 1.21E-25 3.37E-26 1.02E-26
7177.5405 7200.4790 7224.7620 7247.4463 7257.7924 7258.8775 7265.9314 7275.3433 7278.6838 7279.2866 7293.3759
4.96E-26 2.42E-26 8.27E-26 9.76E-26 1.05E-25 1.21E-26 1.02E-25 1.08E-25 3.23E-25 5.65E-26 3.05E-25
7315.2919 7360.6218 7360.8162 7371.5639 7386.9183 7392.8410 7397.2415 7401.5442
1.82E-25 1.61E-25 1.61E-25 4.03E-25 1.01E-25 1.74E-25 3.91E-25 9.08E-26
Exp. pos.b (cm 1) 6906.3279 6911.8503 6912.0678 6940.1080 6942.6829 6959.1639 6969.9340 6989.3073 6995.1889 6995.3944 6995.3950 Not water 7069.5474 7083.0081 7130.3111 7130.3078 7177.5419 7200.4760 7224.7640 7247.4474 7257.7936 7258.8788 7265.9409 7275.3478 7278.6834 7279.2861 7293.3772 7293.3796 7315.2931 7360.6208 7360.8151 7371.5630 Not water 7392.8409 7397.2394 7401.5495
SP Int.c
Elow (cm 1)d
ISOe
Rovibrational assignment
2.48E-26 1.69E-26 6.66E-26 1.63E-25 6.33E-26 1.91E-25 2.61E-26 8.31E-26 7.39E-26 1.59E-26 5.31E-27
1551.2051 2327.9143 1437.9689 141.9024 1080.3856 1327.1102 1557.8451 1985.7855 1695.0691 3109.9121 3109.9121
H218O
200 120 120 021 040 120 200 200 120 031 031
11 0 11 000 12 0 12 13 3 10 000 14 2 13 10 3 7 000 10 2 8 4 1 4 000 3 1 3 9 5 5 000 9 2 8 12 1 12 000 11 0 11 13 1 13 000 12 0 12 11 4 8 000 11 5 7 14 4 8 000 11 3 9 7 7 0 010 7 7 1 7 7 1 010 7 7 0
5.00E-26 3.57E-26 4.45E-27 4.09E-27 6.02E-26 4.15E-26 5.81E-26 8.55E-26 1.01E-25 1.44E-26 1.03E-25 1.88E-25 3.78E-25 4.98E-26 1.72E-25 5.72E-26 1.86E-25 1.65E-25 5.49E-26 4.20E-25
2572.1395 2211.1908 1611.6532 1141.6915 1437.9689 1774.6168 1198.1999 2300.6853 2271.7125 1574.4497 583.7778 1960.2077 1985.7855 2251.8628 2254.2843 2254.2844 2054.3691 1907.6160 1907.4518 647.0720
031 210 101 002 120 200 200 200 210 200 002 200 200 210 200 200 021 210 210 021
8 4 4 010 7 4 3 6 1 5 010 6 2 4 10 4 7 000 10 4 6 11 1 10 000 12 2 9 10 5 5 000 10 2 8 11 4 8 000 12 1 11 9 3 6 000 9 2 7 12 6 6 000 12 5 7 6 4 3 010 6 3 4 10 5 6 000 10 4 7 6 1 6 000 7 0 7 12 3 9 000 12 2 10 11 6 6 000 11 5 7 5 5 0 010 5 4 1 10 9 2 000 10 8 3 10 9 1 000 10 8 2 11 7 4 000 10 7 3 4 4 1 010 3 3 0 4 4 0 010 3 3 1 7 5 3 000 6 3 4
1.63E-25 4.23E-25 6.35E-26
601.9608 1293.0186 2129.5994
H217O
H218O 16
HD O
H218O
H218O H218O
H217O H217O
002 7 1 7 000 6 2 4 120 11 4 8 000 10 1 9 210 5 5 0 010 4 4 1
a
Line intensity (cm 1/ molecule cm 2 at 296 K) from HITRAN database [1]. Line position (cm 1) calculated from experimental energy levels. c SP calculated line intensity (cm 1/ molecule cm 2 at 296 K) [9,11]. d Experimental value (cm 1) of the lower energy level. e Isotopologue, if not H216O. b
It is difficult to analyze systematically the origin of the large values of the 9nCRDS–nIUPAC9 differences. Part of them is due to the lack of precision of the energy level determination when it relies from a single transition. For instance, the IUPAC term value of the (200) 93 7 level 17 of H2 O relies on a single transition reported in Ref. [19] and is shifted by about 0.013 cm 1 from our value (see Section 3.3 and Table 2). In the same time, there are situations when the IUPAC task group used several transitions from different experimental sources but obtained inaccurate energy levels. As an example, we consider the (021) 83 6 level of H217O obtained by Toth [19] from a single transition corresponding to a blended line. As mentioned in Section 3.3, our value is 0.014 cm 1 higher than Toth’s value. The value recommended by the IUPAC task group [12] was obtained from three transitions reported in Refs. [1,19,21] but they were weighted according to different precision values: 0.001 cm 1 for Ref. [19] and 0.010 cm 1 for Refs. [1,21]. As a result, the
IUPAC energy level value is mainly determined by the line position of Ref. [19] which is actually inaccurate. Consequently, the line positions of Ref. [21] reaching the (021) 83 6 level (2n2 þ n3 83 6–95 5 and 2n2 þ n3 83 6–93 7) deviate by 0.0114 and 0.0145 cm 1, respectively while they were both used for the determination of the IUPAC energy level. The difference between the CRDS and IUPAC line positions of the 2n2 þ n3 83 6–73 5 is also about 0.014 cm 1 confirming that the IUPAC weighting is incorrect. 5.3. Comparison to emission spectra The emission spectrum of water vapor has been studied in our region by Zobov et al. [14]. The line list of Ref. [14] contains more than 4100 H216O transitions between 6885 and 7406 cm 1. We compared 1094 positions reported by Zobov et al. [14] to the absorption measurements of Refs. [4–7] and of the present study. The differences range between 0.08 and þ0.08 cm 1. The average difference
O. Leshchishina et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 113 (2012) 2155–2166
2163
Table 5 Corrections of position, intensity or rovibrational assignments of 81 transitions of the HITRAN list between 6885.79 and 7405.91 cm 1. HITRAN Pos. (1)
Our assignment Int. (2)
Assignment (3)
Exp. Pos. (4)
SP Int. (5)
6928.7453 6935.9826 6955.1750 6964.0592 6976.6451 6985.8910 7008.3642 7014.8352 7028.7531 7064.5059 7073.4298 7075.8118 7091.4224 7131.8923 7132.4493 7135.5490 7141.7914 7143.5322
2.05E-26 1.17E-25 2.42E-25 8.47E-26 3.23E-26 9.60E-26 5.33E-25 5.69E-26 7.67E-25 2.12E-26 6.05E-26 1.61E-25 4.44E-25 9.08E-25 5.49E-26 8.07E-25 9.12E-26 5.24E-25
002 111 120 120 200 120 200 002 200 031 040 101 111 101 120 200 101 021
11 5 7 000 12 6 7 6 1 010 8 6 9 3 7 000 9 2 12 1 12 000 11 0 11 4 8 000 11 5 15 0 15 000 14 1 7 1 7 000 6 4 7 3 5 000 7 6 9 4 6 000 9 5 6 5 2 010 5 5 5 5 1 000 4 0 5 0 5 000 4 4 7 3 4 010 6 5 9 1 9 000 8 3 9 6 3 000 10 3 8 1 8 000 7 2 13 6 7 000 13 6 13 1 12 000 12 1
6 2 8 11 7 14 2 2 5 1 4 0 1 6 8 5 8 11
6918.3619 6935.9624 6958.8835 6959.1639 6989.3073 6985.9849 7008.3643 7014.8347 7028.7528 7064.0700 7073.4286 7075.8115 7091.4291 7131.8927 7132.4489 7135.5492 7146.4318 7144.0325
1.09E-26 1.93E-27 9.43E-26 1.91E-25 8.31E-26 7.09E-27 2.10E-29 1.82E-27 2.26E-26 1.28E-26 4.55E-28 6.26E-27 2.67E-27 2.06E-26 3.18E-27 2.23E-26 1.29E-26 5.37E-25
7143.7130 7153.5367 7172.3062 7185.5770 7194.4825 7196.6953 7223.6495 7224.8419 7259.7206 7266.2356 7266.2368 7276.6492 7280.0156 7305.2434 7318.6601 7352.3253 7370.5604 7375.1013 7388.6202 7404.9363 7405.7177
2.06E-26 4.44E-26 1.41E-25 1.13E-23 4.48E-25 1.61E-25 4.03E-26 3.19E-26 5.37E-26 4.03E-24 4.03E-25 6.05E-26 4.84E-25 4.03E-25 2.02E-25 2.02E-26 7.71E-26 1.98E-24 5.12E-26 1.91E-25 2.73E-25
021 210 120 200 200 021 002 002 210 101 002 200 120 101 210 021 031 012 021 111 012
97 42 11 4 61 12 3 13 3 11 5 11 6 51 93 31 12 3 94 93 82 96 85 20 87 11 6 52
3 000 10 5 6 3 010 3 3 0 7 000 12 1 12 6 000 5 2 3 9 000 13 2 12 11 000 12 3 10 7 000 11 6 6 5 000 12 5 8 5 010 4 0 4 6 000 9 3 7 3 000 4 2 2 9 000 12 2 10 6 000 9 1 9 7 000 10 1 10 7 010 7 1 6 4 000 10 2 9 3 010 7 3 4 2 010 2 1 1 1 000 8 5 4 6 010 11 4 7 4 010 4 3 1
7143.7126 7153.5374 7173.5698 7185.5771 7193.1810 7196.6934 7213.2662 7224.8431 7259.7259 7266.2357 7266.2369 7275.3478 7280.0156 7305.2436 7318.6583 7352.3256 7370.5575 7375.1014 7388.6204 7404.9364 7405.7204
2.35E-27 6.53E-27 7.34E-27 2.26E-24 1.22E-26 6.52E-25 7.02E-27 6.25E-28 1.88E-25 7.95E-26 3.66E-24 1.88E-25 8.62E-26 1.42E-25 5.91E-26 5.12E-29 2.93E-26 6.35E-27 5.86E-29 o 1.00E-30 1.40E-28
H218O 6906.4694
2.31E-26
200 11 0 11 000 12 1 12
6906.3279
2.48E-26
6957.7789 6960.0437 7026.4115
3.37E-26 2.21E-26 4.92E-26
101 7 3 5 000 7 5 2 021 9 4 6 000 10 2 9 101 7 1 6 000 6 5 1
6957.7795 6960.0439 7026.4126
4.57E-27 7.05E-27 1.00E-28
7069.5805 7074.7307 7074.8370 7103.5223 7110.0282 7111.8231 7128.9058 7146.8163
1.46E-26 2.02E-25 2.42E-26 1.74E-25 6.05E-26 9.32E-27 1.48E-26 1.34E-26
002 021 002 021 002 101 101 200
6 8 7 4 6 6 7 7
1 3 3 4 2 3 3 1
6 6 5 0 5 4 5 7
000 000 000 000 000 000 000 000
7 7 8 4 7 5 6 6
2 3 4 2 3 5 5 2
5 5 4 3 4 1 2 4
7069.2660 7074.7307 7074.8369 7103.5232 7110.0290 7111.8236 7128.9063 7146.8175
1.56E-26 5.95E-26 5.77E-27 1.27E-27 1.34E-26 1.42E-28 8.37E-29 1.38E-28
7169.4121 7175.7246 7204.8401 7266.2555 7279.3803 7281.9030 7293.8720
2.30E-26 6.90E-26 2.88E-26 9.88E-26 2.06E-25 7.42E-25 6.25E-25
200 002 002 002 002 200 200
6 7 2 6 7 7 8
1 2 0 1 3 2 2
6 5 2 6 5 6 7
000 000 000 000 000 000 000
5 8 3 7 7 7 8
2 3 3 0 4 1 1
3 6 1 7 4 7 8
7169.4127 7175.7308 7204.8404 7265.9409 7279.3802 7281.9031 7293.8721
3.09E-27 9.58E-27 1.01E-28 1.03E-25 5.79E-27 7.37E-26 1.03E-25
Exp. Pos. (6)
SP Int. (7)
ISO (8)
Assignment (9)
H216O Not water Not water Not water 6964.0627 6976.6485 6985.8918
8.85E-26 3.48E-27 9.913E-26
7064.5122
3.34E-26
120 12 0 12 000 11 1 11 210 6 4 3 010 6 5 2 040 12 3 10 000 11 0 11
031 6 5 1 010 5 5 0 18
7075.8160 7091.4344
1.26E-25 4.39E-25
H2 O
7141.7871 7143.5308 7143.5384
1.46E-25 3.71E-25 1.97E-25
002 10 2 8 000 11 3 9 002 11 1 10 000 12 2 11 002 8 2 6 000 8 5 3
7172.3072
1.27E-25
021 15 2 14 000 14 2 13
101 8 1 7 000 8 3 6 021 15 1 15 000 14 1 14
Not water 7223.6468
4.37E-26
040 14 5 10 000 13 2 11
7276.6406
5.03E-26
120 8 4 5 000 7 1 6
7352.3150
1.57E-26
7375.1012
1.98E-24
002 4 0 4 000 3 3 1
7405.7229
1.51E-25
200 13 3 11 000 12 2 10
6906.4583 6906.4780
8.34E-27 7.40E-27
200 11 1 11 000 12 0 12 101 10 4 7 000 11 4 8
7026.4174 7026.4178
4.64E-26 1.55E-26
021 7 7 1 000 7 7 0 021 7 7 0 000 7 7 1
7074.7411
1.51E-25
Not water H216O 210 5 0 5 010 5 1 4
7103.5245
1.83E-25
H216O
120 9 6 4 000 9 5 5
7111.8197
3.69E-27
17 H2 O
200 6 5 1 000 7 4 4
7146.8130 7146.8155 7146.8185
2.83-27 9.43E-28 8.16-27
7266.2566 7279.3823
1.37E-25 1.52E-25
HD16O H216O
002 2 0 2 000 1 1 1 021 13 5 9 000 12 5 8
7293.8663 7293.8692
8.87E-24 4.52E-25
H216O H216O
002 8 3 6 000 8 4 5 021 10 7 4 000 9 7 3
HD16O
002 10 5 5 000 9 5 4
002 11 0 11 000 12 1 12 002 11 1 11 000 12 0 12 111 1 1 1 010 2 1 2
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Table 5 (continued ) HITRAN Pos. (1)
Our assignment Int. (2)
Assignment (3)
Exp. Pos. (4)
SP Int. (5)
7303.5059 7308.2219 7338.0350 7347.8724 7357.7665 7404.8748
2.20E-26 4.84E-26 7.42E-26 5.77E-26 3.93E-26 3.06E-26
021 021 200 200 200 002
8 3 6 000 7 1 7 5 5 1 000 4 3 2 4 3 2 000 3 2 1 11 0 11 000 10 1 10 12 1 12 000 11 0 11 6 1 6 000 5 2 3
7303.5059 7308.2219 7338.0352 7347.7307 7357.4541 7404.5602
1.53E-27 1.76E-27 8.18E-28 6.33E-26 2.44E-26 2.61E-26
H217O 6908.4716 6977.1542 6989.7377 7013.3049 7136.0347 7215.8081 7277.5076 7278.1270 7322.7163 7344.9030 7366.2690
1.36E-26 8.07E-27 2.00E-26 4.32E-26 8.71E-27 5.04E-27 3.00E-25 1.81E-26 4.52E-26 3.61E-26 9.76E-26
200 101 021 002 200 002 200 200 200 200 101
80 11 1 75 20 62 61 80 10 1 66 80 11 1
8 000 10 000 3 000 2 000 5 000 6 000 8 000 10 000 0 000 8 000 10 000
HD16O 6912.2569 7196.6979 7260.2314 7301.1096 7311.4705 7353.0972
6.41E-26 1.17E-25 2.02E-25 2.39E-26 1.99E-25 3.09E-25
210 002 002 002 002 002
63 95 62 43 52 14 2
4 5 4 2 4 12
9 1 11 3 65 33 6 1 70 71 90 73 9 1 11 3
9 9 2 1 6 7 7 9 5 9 9
6908.4735 6977.0874 6989.8554 7013.4406 7134.5576 7215.8072 7277.5084 7277.9879 7322.8339 7346.1128 7366.2690
4.41E-27 4.64E-28 2.16E-26 3.65E-28 1.04E-26 1.49E-29 7.81E-26 1.92E-26 4.71E-26 3.19E-26 2.23E-30
000 5 2 000 9 5 000 6 2 000 5 1 000 5 0 000 14 1
3 4 5 5 5 13
6912.2570 7196.6979 7260.2314 7301.1098 7311.4704 7353.0974
1.20E-27 1.19E-26 6.45E-26 3.66E-32 2.22E-26 4.52E-28
Exp. Pos. (6)
SP Int. (7)
ISO (8)
Assignment (9)
7293.8798
1.36E-24
H216O
021 10 7 3 000 9 7 2
7347.8736 7357.7619 7404.8742
2.15E-26 1.19E-28 1.29E-26
H216O H216O
200 11 1 11 000 10 0 10 002 13 4 9 000 14 3 12 050 13 0 13 000 12 3 10
Not water 7013.3059 7136.0354
4.44E-26 6.41E-26
H216O
002 7 1 7 000 8 2 6 002 5 2 3 000 5 5 0
7277.5167
1.21E-25
H218O
200 2 2 0 000 1 1 1
Notations: (1), (2), and (3) are line position (cm 1), line intensity (cm 1/ molecule cm 2 at 296 K), and vibration–rotation assignment of the upper and lower levels from HITRAN database [8]. (4)—line position (cm 1) calculated from experimental energy levels of the transition given in column (3). (5)—SP calculated line intensity (cm 1/ molecule cm 2 at 296 K) of the transition given in column (3). (6)—line position (cm 1) calculated from experimental energy levels of the transition given in column (9). (7)—SP calculated line intensity (cm 1/ molecule cm 2 at 296 K) of the transition given in column (9). (8)—isotopologue if different from HITRAN. (9)—our vibration–rotation assignment.
Fig. 7. Comparison of the CRDS spectrum of water vapor recorded at 0.1 Torr to the corresponding simulation using the HITRAN line list showing two examples of ‘‘phantom’’ lines (markedn) included in the HITRAN database [8] but absent in the CRDS spectrum. In fact, the position of the two problematic lines is correct but their HITRAN intensity is overestimated by several orders of magnitude (see Table 5).
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2165
Fig. 9. Upper panel: CRDS (this work) and HITRAN line lists for water between 6885 and 7408 cm 1. Lower panel: Corresponding ‘‘complete’’ line list calculated from the experimentally determined energy levels combined to variational intensities (intensity cut off of 1 10 28 cm/molecule at 296 K).
Fig. 8. Histograms of the differences between the CRDS line positions of H218O, H217O, and HD16O and those calculated by using the IUPAC energy levels [12,13].
is 0.0017 cm 1 and the rms value is 0.0158 cm 1. Using all available H216O experimental energy levels, 2158 line positions can be calculated and compared to those of Ref. [14]. The differences range from -0.29 to þ0.37 cm 1 in this case and the room mean square deviation is 0.0208 cm 1. This rms value agrees with the average uncertainty claimed in Ref. [14] for the spectra obtained with a torch at atmospheric pressure. It confirms that as a result of the line broadening and blends (and then multiple assignments for many lines), hot spectra can hardly be used for accurate determination of energy levels. 5.4. A ‘‘complete’’ line list for water in the 6885–7408 cm 1 region In order to provide the most complete line list in the region, a list of 12,700 transitions for water in ‘‘natural’’ isotopic abundance is given as Supplementary Material (Sup_Mat_3.txt file). The intensity cut off was fixed to 1 10 28 cm/molecule. Most of the line positions were calculated from the experimental values of the energy levels and associated intensities at 296 K are the variational values [9]. Above the chosen intensity cut off, 525
weak transitions reach upper energy levels which are not yet experimentally determined. In those situations, we reproduced SP line positions. The corresponding line positions (marked SP) may deviate significantly (up to 0.3 cm 1) from their real values. Some of these SP line positions could be corrected on the basis of the general tendency of the (obs.–calc.) deviations of the series of upper energy levels (the corresponding transitions are marked ‘‘estimation’’). Fig. 9 shows an overview of the ‘‘complete’’ line list compared to the HITRAN and CRDS lists. 6. Conclusion The spectroscopic parameters of more than 4900 water transitions were measured by CRDS between 6885 and 7408 cm 1. As a result of the sensitivity of the CRDS recordings and of the use of low pressure values (typically 0.1 Torr) about 1300 medium and weak lines could be newly detected. The minimum intensity values are on the order of 5 10 28 cm/molecule i.e. between one and two orders of magnitude lower than the HITRAN intensity cut off for H216O in the investigated region. The gain is particularly important for the major isotopologue and the H217O species. The rovibrational analysis was performed by using the previously obtained experimental energy levels as well as calculated spectra of different water species. Finally, 21 new and corrected energy levels belonging to four vibrational states of H217O and H218O were determined from the vibration–rotation analysis. The analysis led to new or corrected assignments for more than one hundred lines included in the HITRAN database [8] (see Tables 4, 5 and Sup_Mat_2.txt file).
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A few inaccuracies in the energy sets of the IUPAC task group [12] were evidenced and corrected. Nevertheless, the critical review and validation of the energy levels performed by the IUPAC task group for H217O, H218O, HD16O, HD17O, and HD18O [12,13] represent a considerable improvement compared to the present status of the HITRAN database, both in terms of completeness and accuracy. A major result of the present work is the construction of a ‘‘complete’’ list of 12,700 transitions for water in ‘‘natural’’ abundance between 6885 and 7408 cm 1 (intensity cut off of 1 10 28 cm 1/ molecule cm 2 at 296 K).
[8]
[9] [10]
[11]
[12]
Acknowledgments [13]
This work is jointly supported by CNRS (France) and RFBR (Russia) in the in the frame of Groupement de Recherche International SAMIA (Spectroscopie d’Absorption des Mole´cules d’Inte´rˆet Atmosphe´rique), as well as by RFBR-CNRS Grant no. 10-05-93105. The work of S.M. was also partly supported by the program 3.9.6 of the Russian Academy of Sciences (RAS) and by the program 22 ‘‘Fundamental problems of the Solar system studies’’ of the Presidium RAS. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j. jqsrt.2012.06.026.
[14]
[15]
[16]
[17] [18]
[19] [20]
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