Global modeling of OCO and OCO absolute line intensities in the 1.35 μm region

In our recent contribution, (K.F. Song, S. Kassi, S.A. Tashkun, V.I. Perevalov, A. Campargue, J. Quant. Spectrosc. Radiat. Transf. 111 (2010) 332-344), line intensities have been measured for 2 and 6 bands of the ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O isotopologues detected in the range 7123-7917 cm⁻¹ using Cavity Ring Down Spectroscopy. The present note describes the global fitting of these measured intensities, and derivation of sets of effective dipole moment parameters for these isotopologues. These parameters allow reproducing the intensities of the measured very weak lines (2 × 10⁻²⁹-7 × 10⁻²⁸ cm/molecule) with an RMS of residuals on the order of 6%.     

Spectroscopic database of CO2 line parameters: 4300-7000 cm

A new spectroscopic database for carbon dioxide in the near infrared is presented to support remote sensing of the terrestrial planets (Mars, Venus and the Earth). The compilation contains over 28,500 transitions of 210 bands from 4300 to 7000 cm⁻¹ and involves nine isotopologues: ¹⁶O¹²C¹⁶O (626), ¹⁶O¹³C¹⁶O (636), ¹⁶O¹²C¹⁸O (628), ¹⁶O¹²C¹⁷O (627), ¹⁶O¹³C¹⁸O (638), ¹⁶O¹³C¹⁷O (637), ¹⁸O¹²C¹⁸O (828), ¹⁷O¹²C¹⁸O (728) and ¹⁸O¹³C¹⁸O (838). Calculated line positions, line intensities, Lorentz half-width and pressure-induced shift coefficients for self- and air-broadening are taken from our recent measurements and are presented for the Voigt molecular line shape. The database includes line intensities for 108 bands measured using the McMath-Pierce Fourier transform spectrometer located on Kitt Peak, Arizona. The available broadening parameters (half-widths and pressure-induced shifts) of ¹⁶O¹²C¹⁶O are applied to all isotopologues. Broadening coefficients are computed using empirical expressions that have been fitted to the experimental data. There are limited data for the temperature dependence of widths and so no improvement has been made for those parameters. The line intensities included in the catalog vary from 4×10⁻³⁰ to 1.29×10⁻²¹ cm⁻¹/(molecule cm⁻²) at 296 K. The total integrated intensity for this spectral interval is 5.9559×10⁻²⁰ cm⁻¹/(molecule cm⁻²) at 296 K.     

High sensitivity CW-CRDS spectroscopy of CO2, OCO and OCO between 5851 and 7045 cm: Line positions analysis and critical review of the current databases

The exhaustive line positions analysis of the absorption spectrum of carbon dioxide in natural abundance has been performed on the basis of high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 7045 cm⁻¹ (1.71-1.42 μm). The achieved sensitivity (noise equivalent absorption α_min ∼ 2-5 × 10⁻¹⁰ cm⁻¹) have allowed the detection of 8293 transitions of the ¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O isotopologues. They belong to a total of 130 bands. Line intensities of the weakest transitions are on the order of 2 × 10⁻²⁹ cm/molecule. The rovibrational assignments were performed on the basis of accurate predictions of the effective Hamiltonian model of the respective isotopologues. The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 121 bands from a fit of the measured line positions. A number of resonance interactions were identified. In particular, the first observation of an interpolyad coupling is reported for the ¹⁶O¹²C¹⁸O isotopologue. The results of the complete line positions analysis are provided as Supplementary material.The obtained experimental dataset which is the most complete in the considered region, has been used for a critical review of the most currently used spectroscopic databases of carbon dioxide: HITRAN, GEISA, HITEMP, and the recent JPL and CDSD databases.     

High sensitivity CW-cavity ring down spectroscopy of CO2 near 1.35 μm (II): New observations and line intensities modeling

In a previous contribution [Kassi S, Song KF, Campargue A. High sensitivity CW-cavity ring down spectroscopy of ¹²CO₂ near 1.35 μm (I): line positions. JQSRT 110 (2009) 1801-1814], the line positions analysis of the high sensitivity absorption spectrum of carbon dioxide has been reported in the 7123-7793 cm⁻¹ region. In this second contribution, the spectral region investigated by CW-cavity ring down spectroscopy has been extended up to 7917 cm⁻¹. It added about 400 lines to our previous list of about 2500 transitions. These additional lines include transitions belonging to six newly observed ¹²C¹⁶O₂ bands for which we provide the spectroscopic parameters. Over the whole 7123-7917 cm⁻¹ region, the accurate intensities of about 2900 lines belonging to four isotopologues (¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹⁶O¹²C¹⁸O and ¹⁶O¹²C¹⁷O) were retrieved with an average accuracy of 3%. Intensity values range between 1.2×10⁻²⁹ and 4.1×10⁻²⁵ cm/mol. Compared to the present version of the carbon dioxide spectroscopic databank recently adopted for the HITRAN database, important deviations were evidenced for some weak bands of the main isotopologue. The CW-CRDS intensity data relative to a total of 46 ¹²C¹⁶O₂ bands together with selected intensity information available in the literature for nine bands have been fitted simultaneously using the effective operators approach. The ΔP=11 set of the ¹²C¹⁶O₂ effective dipole moment parameters has been refined leading to a much better agreement with the measured intensity values. In addition, the ΔP=10 effective dipole moment parameters of the ¹⁶O¹²C¹⁸O minor isotopologue were determined for the first time. The obtained results will help to improve the carbon dioxide spectroscopic databank (CDSD).     

CW-cavity ringdown spectroscopy of carbon dioxide isotopologues near 1.5 μm

The absorption spectra of carbon dioxide in natural isotopic abundance and with 99% enrichment in ¹³C have been recorded by CW-cavity ringdown spectroscopy in two specific spectral regions: 5957-6122 and 6745-6833 cm⁻¹. The spectra were obtained at Doppler limited resolution by using a CW-CRDS spectrometer based on fibered DFB lasers. The typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹, allowed for the detection of lines with intensity as weak as 5 × 10⁻²⁹ cm/molecule. More than 2900 line positions of the six major isotopologues contributing to the spectra (¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O, ¹⁶O¹²C¹⁸O, ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O and ¹⁶O¹³C¹⁸O), were measured and assigned on the basis of their respective global effective Hamiltonian models. For comparison, only 507 lines are provided by the HITRAN database in these spectral regions. The band by band analysis has led to the determination of the rovibrational parameters of a total of 52 bands, 30 of them being newly reported. Most of the observed line positions show an agreement close to the experimental uncertainty (1-2 × 10⁻³ cm⁻¹) with the predictions of their respective effective Hamiltonian models. However, the quality of the predictions degrades for the minor isotopologues reaching maximum deviations of 0.35 cm⁻¹ in one specific case. For several bands, rovibrational transitions with J values between 60 and 90 could be newly detected. While an excellent agreement is observed with the line positions predicted by the Hamiltonian models, the comparison of these observations with the line positions listed in the HITRAN database or extrapolated by using the best FTS rotational constants available in the literature has evidenced significant deviations.     

High sensitivity CW-Cavity Ring Down Spectroscopy of five CO2 isotopologues of carbon dioxide in the 1.26-1.44 μm region (I): Line positions

The absorption spectrum of highly enriched ¹³C carbon dioxide has been investigated by CW-Cavity Ring Down Spectroscopy with a setup based on fibered distributed feedback (DFB) laser diodes. By using a series of 30 DFB lasers, the CO₂ spectrum was recorded in the 7029-7917 cm⁻¹ region with a typical sensitivity of 3×10⁻¹⁰ cm⁻¹. The uncertainty on the determined line positions is on the order of 8×10⁻⁴ cm⁻¹. More than 3800 transitions with intensities as low as 1×10⁻²⁹ cm/molecule were detected and assigned to the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O, ¹⁶O¹³C¹⁸O, ¹⁷O¹³C¹⁸O and ¹³C¹⁸O₂ isotopologues. For comparison, only 104 line positions of ¹³C¹⁶O₂ were previously reported in the literature in the considered region. The band-by-band analysis has led to the determination of the rovibrational parameters of a total of 83 bands including 56 bands of the ¹³C¹⁶O₂ species. The measured line positions of ¹³C¹⁶O₂ and ¹⁶O¹³C¹⁸O were found in good agreement with the predictions of the respective effective Hamiltonian (EH) models but the agreement degrades for the minor isotopologues. Several cases of resonance interactions were found and discussed. In the 20033-10002 band of ¹³C¹⁶O₂, an anharmonic resonance interaction leads to deviations on the order of 0.05 cm⁻¹ compared to the EH predictions. The existence of interpolyad interactions affecting the non-symmetric isotopologues of carbon dioxide is confirmed by the observation of two occurrences in ¹⁶O¹³C¹⁷O and ¹⁶O¹³C¹⁸O. The obtained results improve significantly the knowledge of the spectroscopy of the ¹³C isotopologues of carbon dioxide. They will be valuable to refine the sets of effective Hamiltonian parameters used to generate the CDSD database.     

Near infrared spectroscopy of carbon dioxide. II: OCO and OCO line positions

High-resolution near-infrared (4000-8500 cm⁻¹) spectra of ¹³C-enriched carbon dioxide have been recorded using the McMath-Pierce Fourier transform spectrometer at the Kitt Peak National Solar Observatory. We observed over 1000 line positions for the ¹⁶O¹³C¹⁶O isotopologue, the majority of which have previously been observed only in spectra of the Venusian atmosphere [J. Mol. Spectrosc. 67 (1977) 304]. These have been analyzed to determine spectroscopic constants for 28 different vibrational states. The analysis yielded RMS fitting residuals <1.5 × 10⁻⁴ cm⁻¹ for the strongest bands and RMS residuals <5 × 10⁻⁴ cm⁻¹ for most other fitted bands. A 5% ¹⁸O-enrichment in the sample enabled us to observe 410 line positions from 5 near-infrared vibrational bands of the ¹⁶O¹³C¹⁸O isotopologue. Analysis of the ¹⁶O¹³C¹⁸O bands yielded RMS fitting residuals <2 × 10⁻⁴ cm⁻¹. Additionally, the first fits for the ¹⁶O¹³C¹⁸O 11101 ← 01101 and 11102 ← 01101 hot bands yielded RMS residuals of 2.3 × 10⁻⁴ and 2.2 × 10⁻⁴ cm⁻¹, respectively. Critical reevaluations of the spectroscopic constants for the low lying vibrational states for both isotopologues have been performed as part of the analysis.     

A (nearly) complete experimental linelist for CO2, OCO, OCO, CO2 and OCO by high-sensitivity CW-CRDS spectroscopy between 5851 and 7045 cm

An experimental database for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O, ¹⁶O¹³C¹⁷O, ¹³C¹⁸O₂ and ¹⁷O¹³C¹⁸O isotopologues of carbon dioxide has been constructed on the basis of the high-sensitivity absorption spectrum of carbon dioxide with 99% enrichment in ¹³C recorded by CW-cavity ring down spectroscopy (CW-CRDS) between 5851 and 7045 cm⁻¹. As a result of the achieved sensitivity (typical noise equivalent absorption α_min∼2-5×10⁻¹⁰ cm⁻¹) combined with the high linearity and dynamics (more than four decades) of the CW-CRDS technique, the amount of spectroscopic information contained in these spectra was considerable. A total of 8639 transitions of the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O, ¹⁶O¹³C¹⁷O, ¹³C¹⁸O₂ and ¹⁷O¹³C¹⁸O isotopologues with line strength as low as 5×10⁻²⁹ cm/molecule were assigned. They belong to a total of 150 bands, while less than 20 bands were previously reported by Fourier transform spectroscopy. The excellent agreement between the predictions of the effective operators model and the observations has allowed using an automatic search program to assign the weaker lines observed in the congested spectrum. The spectroscopic parameters of the vibrational upper levels were obtained from a fit of the measured line positions. A number of resonance interactions were observed; in particular, several occurrences of interpolyad anharmonic couplings not included in the polyad model of effective Hamiltonian, were found to affect a few bands of the ¹⁶O¹³C¹⁸O and ¹⁶O¹³C¹⁷O isotopologues. In the list of 8639 transitions, which are provided as Supplementary material, line positions are experimental values (typical uncertainty in the order of 1×10⁻³ cm⁻¹), while line strengths were calculated at 296 K by using the effective operators approach (typical uncertainty in the order of 5%). In the case of the ¹³C¹⁶O₂ isotopologue, the reported transitions represent 99.65% of the total absorbance in the region considered.     

Global effective Hamiltonians of OCO and OCO improved from CW-CRDS observations in the 5900-7000 cm region

The parameters of the polyad models of the effective Hamiltonian of the ¹⁶O¹³C¹⁷O and ¹⁶O¹³C¹⁸O isotopologues of carbon dioxide have been refined by the least-squares fittings to the line positions collected from the literature. Such refinement has become necessary as the observed dataset has been significantly extended by our CW-CRDS observations in the 5900-7000 cm⁻¹ region. In the case of the ¹⁶O¹³C¹⁷O isotopologue, 1151 line positions of 11 bands have been used to refine the effective Hamiltonian parameters published by Chédin [A. Chédin, J. Mol. Spectrosc. 76 (1979) 430-491]. With the obtained set of parameters, the collected line positions are reproduced with a RMS (root mean squares of the residuals) equal to 0.0013 cm⁻¹. In the case of the ¹⁶O¹³C¹⁸O isotopologue, 61 parameters of the effective Hamiltonian were fitted to more than 6410 line positions. A weighted standard deviation of χ = 1.77 and a global RMS of 0.0017 cm⁻¹, close to the experimental accuracy, were achieved. However, several rotational levels of the 31113 state (P = 10) could not be reproduced in the frame of this polyad model and were then excluded from the fit. We found that these levels are affected by an anharmonic resonance interaction with the 51106 vibrational state (P = 11) leading to energy shifts up to 0.060 cm⁻¹ and significant intensity transfer to several extra lines which could be detected. The coupling matrix element has been estimated to 0.11 cm⁻¹ from the detailed analysis of the experimental spectrum. This is the first evidence of an interpolyad resonance interaction in the case of the carbon dioxide molecule. In order to extend the input spectroscopic information, the weak lines left unassigned in our previous analysis of the CW-CRDS spectrum of the ¹³C enriched carbon dioxide [Y. Ding, P. Macko, D. Romanini, V.I. Perevalov, S.A. Tashkun, J.-L. Teffo, S.-M. Hu, A. Campargue, J. Mol. Spectrosc. 226 (2004) 146-160.] have been revisited. Thirteen ¹³C¹⁶O₂ bands, one ¹⁶O¹³C¹⁷O band and two ¹⁶O¹³C¹⁸O bands could be newly assigned together with a number of transitions corresponding to high J values of previously observed bands. The spectroscopic constants G_v, B_v, and D_v for the unperturbed bands have been fitted to the observed line positions.     

Line positions and strengths of OCO, OCO and OCO between 2200 and 7000 cm

Line positions and strengths of ¹⁶O¹²C¹⁸O (628), ¹⁸O¹²C¹⁸O (828) and ¹⁷O¹²C¹⁸O (728) were measured between 2200 and 7000 cm⁻¹ using 22 near infrared (NIR) absorption spectra recorded at 0.01-0.013 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. These data were obtained at room temperature using absorption cells with optical path lengths ranging from 2.4 to 385 m; the cells were filled with natural and ¹⁸O-enriched samples of CO₂ at pressures ranging from 0.54 to 252 torr. The observed line positions were analyzed to obtain the upper state band centers and rotational constants for 17 bands of ¹⁶O¹²C¹⁸O, 19 bands of ¹⁸O¹²C¹⁸O and 8 bands of ¹⁷O¹²C¹⁸O. The majority of the ¹⁸O¹²C¹⁸O and ¹⁷O¹²C¹⁸O bands were measured for the first time. In addition, the rotational constants for the lower states 00001, 01101e and 01101f were derived for all three species using the method of combination differences in which the averaged values obtained from the line positions of two or more bands were least-squares-fitted. Rovibrational parameters were also obtained for the 02201e, 02201f, 10002 and 10001 states of ¹⁸O¹²C¹⁸O. The line position analysis revealed that transitions of the levels 38 ? J′ ? 46 of the 11111f ← 01101f band of ¹⁸O¹²C¹⁸O are perturbed. Perturbed transitions were also observed for the 12212 ← 02201 band and in the high-J transitions (J′ ? 49) of the 20012 ← 00001 band of ¹⁸O¹²C¹⁸O. Band strengths and Herman-Wallis-like F-factor coefficients were determined for 21 bands of ¹⁶O¹²C¹⁸O, 25 bands of ¹⁸O¹²C¹⁸O and 8 bands of ¹⁷O¹²C¹⁸O from least-squares fits to more than 3700 measured transition intensities; band strengths and line positions for 34 of these bands were obtained for the first time.