High sensitivity cavity ring down spectroscopy of CO2 overtone bands near 790 nm

The dyad bands of near 790 nm have been recorded with a continuous-wave cavity ring-down spectrometer. Two cold bands and the two associated hot bands are observed in this region. High sensitivity of the 1×10⁻¹⁰/cm level allows one to detect weak transitions with satisfied accuracy. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for majority of the unblended lines. The vibrational transition dipole moment squared values and the empirical Herman-Wallis coefficients are presented for two cold bands. The comparison of the retrieved line positions and intensities with those given in the Carbon Dioxide Spectroscopic Databank shows clear deviation and indicates the empirical calculation can be further improved using the present spectroscopy data.     

Line parameters for the 01111-00001 band of COO from SOIR measurements of the Venus atmosphere

CO₂ is the major constituent of the atmosphere of Venus. Absorption lines due to its ¹²C¹⁶O¹⁸O isotopologue have been observed for the first time in Venus spectra in the 2930-3015 cm⁻¹ spectral region, where the HITRAN database does not contain any line from this isotopologue. The measurements were performed by the SOIR instrument, which is part of the SPICAV/SOIR instrument on board the Venus Express mission of ESA. SOIR measured the atmospheric transmission of the upper atmosphere of Venus (z>70 km) by performing a solar occultation experiment using the atmosphere as a gigantic absorption cell. The identification of this newly observed band was first made recently from Mars atmosphere observations by US colleagues. We have made independent theoretical calculations of the positions of the lines of this new 01111-00001 absorption band, which coincide perfectly with the positions of the observed lines. Assuming an oxygen isotopic ratio similar to the one measured previously in the lower atmosphere of Venus, the line strengths of each observed line are deduced and listed.     

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.     

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%.     

CO2 line intensity measurements around 1.6 μm

Using Fourier transform spectra and a multispectrum fitting procedure, 271 absolute line intensities of ¹²C¹⁶O₂ have been measured around 1.6 μm, for the three cold bands 30014-00001, 30013-00001, and 30012-00001, and for the two hot bands 31113-01101 and 31112-01101, extending from 6035 to 6380 cm⁻¹. Accuracies are on the average 3 and 5% for cold and hot bands, respectively. Vibrational transition dipole moments and Herman-Wallis coefficients are reported for each band. Comparisons are made with previous experimental results and with data available in the HITRAN database and the Carbon Dioxide Spectroscopic Databank (CDSD).     

High sensitivity CW-cavity ring down spectroscopy of CO2 near 1.35 μm (I): line positions

The absorption spectrum of carbon dioxide in natural isotopic abundance has been investigated by CW-cavity ring down spectroscopy with a new setup based on fibred distributed feedback (DFB) laser diodes. By using a series of 25 DFB lasers, the CO₂ spectrum was recorded in the 7123–7793 cm⁻¹ region with a typical sensitivity of 3×10⁻¹⁰ cm⁻¹. A 2125 transitions with intensities as low as 1×10⁻²⁹ cm/molecule were detected and assigned to the ¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O isotopologues. For comparison, only 357 of them were previously reported from Venus spectra and 344 transitions were included in the 2004 version of the HITRAN database. The band by band analysis has led to the determination of the rovibrational parameters of 28, 2 and 6 bands for the ¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O isotopologue, respectively. While the uncertainty on the experimental line positions is on the order of 5×10⁻⁴ cm⁻¹, the average deviation from the ¹²C¹⁶O₂ calculated values provided by the most recent version of the carbon dioxide spectroscopic databank (CDSD) is −2.8×10⁻³ cm⁻¹ with an root mean square (rms) deviation of 3.5×10⁻³ cm⁻¹. Maximum deviations in the order of 0.02 and 0.12 cm⁻¹ were evidenced for some bands of the ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O minor isotopologues. The obtained results improve significantly the previous measurements from Venus spectra and will be valuable to refine the sets of effective Hamiltonian parameters used to generate the CDSD database.     

New CW-CRDS measurements and global modeling of CO2 absolute line intensities in the 1.6 μm region

Line intensities of ¹²C¹⁶O₂ transitions have been measured by CW-Cavity Ring Down Spectroscopy in four wavenumber intervals near 1.6 μm. Intensity values of 952 transitions ranging from 1.10 × 10⁻²⁸ to 4.94 × 10⁻²⁵ cm/molecule were retrieved with an average accuracy of 4%. These transitions belong to a total of 30 bands corresponding to the ΔP = 9 series of transitions. The achieved sensitivity (noise equivalent absorption α_min ∼ 3 × 10⁻¹⁰ cm⁻¹) allows lowering by more than two orders of magnitude the lower intensity values measured in the region. Comparison with the values included in the JPL database [R.A. Toth, L.R. Brown, C.E. Miller, V. Malathi Devi, D.C. Benner, J. Quant. Spectrosc. Radiat. Transf. 109 (2008) 906-921] shows residuals exceeding one order of magnitude for weak lines. The measured intensities together with a selection of experimental intensities available in the literature were used to extend and refine the set of effective dipole moment parameters for the ΔP = 9 series of transitions of the principal isotopologue of carbon dioxide. The refined parameters allow reproducing, within the experimental uncertainties, the whole set of intensity measurements which extends over nearly six orders of magnitude (1.10 × 10⁻²⁸-6.12 × 10⁻²³ cm/molecule). Combining the CW-CRDS line positions with the calculated line intensities, a line list has been generated for the whole 5851-7045 cm⁻¹ region and is provided as Supplementary Material. The obtained effective dipole moment parameters have also been used to generate the ΔP = 9 series of transitions included in the new version of the CDSD database. The comparison of the CDSD line intensities with the values provided by the HITRAN-2004 database shows discrepancies up to 80% for some of the bands while discrepancies up to three orders of magnitude are noted for the weakest bands included in the JPL database.     

CDSD-4000: High-resolution, high-temperature carbon dioxide spectroscopic databank

We present a high-resolution, high-temperature version of the Carbon Dioxide Spectroscopic Databank called CDSD-4000. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths, coefficients of temperature dependence of air- and self-broadened half-widths, and air-broadened pressure shifts) of the four most abundant isotopologues of CO₂. A reference temperature is 296 K and an intensity cutoff is 10⁻²⁷ cm⁻¹/molecule cm⁻² at 4000 K. The databank has 628,324,454 entries, covers the 226-8310 cm⁻¹ spectral range and designed for the temperature range 2500-5000 K. Format of CDSD-4000 is similar to that of HITRAN-2008. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. The databank is useful for studying high-temperature radiative properties of CO₂, including exoplanets atmospheres, aerothemal modeling for Mars entry missions, high-temperature laboratory spectra, and industrial applications. CDSD-4000 is freely accessible via the Internet site ftp://ftp.iao.ru/pub/CDSD-4000.     

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.