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.     

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.     

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.     

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-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.     

Fourier transform spectroscopy of CO2 and OCO in the 3800-8500 cm region and the global modeling of the absorption spectrum of CO2

The absorption spectrum of the ¹⁸O enriched carbon dioxide has been recorded at Doppler limited resolution with a Fourier transform spectrometer in the spectral range 3800-8500 cm⁻¹. Seventeen cold bands (14Σ-Σ and 3Σ-Π) and nine hot bands (9Π-Π) of ¹²C¹⁸O₂, nineteen cold bands (18Σ-Σ and 1Σ-Π) and eighteen hot bands (6Σ-Σ, 9Π-Π and 3Δ-Δ) of ¹⁶O¹²C¹⁸O have been observed. Among them, 14 ¹²C¹⁸O₂ bands and 12 ¹⁶O¹²C¹⁸O bands are observed for the first time. The spectroscopic parameters G_v, B_v, and centrifugal distortion constants, have been determined for all observed bands. Effective Hamiltonian parameters for the ¹²C¹⁸O₂ isotopic species are retrieved from the global fitting of the observed line positions presented in this paper and collected from the literature. As the result, 65 obtained effective Hamiltonian parameters reproduce 5443 observed line positions of 73 ¹²C¹⁸O₂ bands with RMS = 0.00145 cm⁻¹.     

OCO: high-resolution absorption spectrum between 4000 and 9500 cm and global fitting of vibration-rotational line positions

The absorption spectrum of a ¹³C enriched carbon dioxide sample has been recorded with a Fourier-transform spectrometer in the spectral range 4000-9500 cm⁻¹. In addition to six bands observed from the spectrum of the atmosphere of Venus in this region, eight new ¹⁶O¹³C¹⁸O bands were measured. The new observations together with the data collected from the literature have been used to fit parameters of an effective Hamiltonian for the ¹⁶O¹³C¹⁸O. More than 4000 line positions in 38 bands have been used to derive 48 parameters of effective Hamiltonian. The RMS (root-mean-square of residuals) of the fit is 0.00106 cm⁻¹.     

Comment on “Spectroscopic database of CO2 line parameters: 4300–7000 cm–1”

The “Spectroscopic database of CO₂ line parameters: 4300–7000 cm^–1” constructed by Toth et al., has been considered in relation with our previous and current studies of the absorption spectrum of carbon dioxide (CO₂) by high-sensitivity CW-cavity ring down spectroscopy (CW-CRDS) in the 5850–7000 cm^?1 region. Part of the line parameters of the database are based on accurate spectroscopic measurements by Fourier transform spectroscopy (FTS) but Toth et al. have chosen to fix to a very low value (4×10^?30 cm/molecule) the lower intensity cut off. This value which is far below the FTS detection limit has led to long range extrapolations to high J values and to the inclusion of weak unobserved bands which were theoretically predicted. In the 5850–7000 cm^?1 region, most of these calculated transitions were previously observed by CW-CRDS. The comparison with the CW-CRDS ¹³CO₂ spectrum in this region, has evidenced that (i) many weak bands above the intensity cut off are missing; (ii) there are important deviations between the line parameters provided in the database and our previous observations both for line positions (up to 1.7 cm^?1) and line intensities (up to a factor 80). Our discussion was limited to the three ¹³C species (¹³C¹⁶O₂, ¹⁶O¹³C¹⁸O and ¹⁶O¹³C¹⁷O) but the conclusions should apply to the other isotopologues in particular ¹²C¹⁶O₂ and to the full spectral range of the database.Alternatively, the global effective operators models for CO₂ can reproduce satisfactorily all the experimental line positions and line intensities available in the literature. This polyad model, which has been developed for most of the CO₂ isotopologues, constitutes an interesting alternative for the most accurate and complete CO₂ database. In particular, very weak bands, accidental resonances, intensity transfers and extra lines are accurately accounted for and predicted by this polyad model.     

High sensitivity cw-cavity ringdown and Fourier transform absorption spectroscopies of CO2

The absorption spectrum of ¹³CO₂ has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130-6750 cm⁻¹ region with a typical sensitivity of 5 × 10⁻¹⁰ cm⁻¹. The spectrum has also been recorded between 4400 and 8500 cm⁻¹ with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105 m). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the ¹³C¹⁶O₂, ¹⁶O¹³C¹⁷O, and ¹⁶O¹³C¹⁸O isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the ¹³C¹⁶O₂ isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14 650 line positions of ¹³C¹⁶O₂ with an RMS=0.002 cm⁻¹. A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed.     

Highly sensitive absorption spectroscopy of carbon dioxide by ICLAS-VeCSEL between 8800 and 9530 cm

The absorption spectrum of carbon dioxide has been studied between 8800 and 9530 cm⁻¹ by intracavity laser absorption spectroscopy based on a vertical external cavity surface emitting lasers (VeCSEL). Previous laboratory spectra at high resolution were nearly absent in the considered spectral region. Experiments were carried with natural carbon dioxide and with ¹³C enriched carbon dioxide leading to the determination of the rovibrational parameters of a total of 15 very weak vibrational transitions, including two bands of the ¹⁶O¹³C¹⁸O isotopologue. The observed transitions are assigned to components of the 2ν₁ + 3ν₃ triad and of the much weaker 5ν₁ + ν₃ hexad. Our measured line positions are found in excellent agreement with the predictions of the effective Hamiltonians developed for ¹²C¹⁶O₂ and ¹³C¹⁶O₂ but significant deviations were evidenced for the ¹⁶O¹³C¹⁸O minor isotopologue. The relative band intensities within each polyad are also discussed on the basis of the effective Hamiltonian model.     

Near infrared spectroscopy of carbon dioxide I. OCO line positions

High-resolution near-infrared (4000-9000 cm⁻¹) spectra of carbon dioxide have been recorded using the McMath-Pierce Fourier transform spectrometer at the Kitt Peak National Solar Observatory. Some 2500 observed positions have been used to determine spectroscopic constants for 53 different vibrational states of the ¹⁶O¹²C¹⁶O isotopologue, including eight vibrational states for which laboratory spectra have not previously been reported. Calibration by simultaneous use of CO near 4200 cm⁻¹ and C₂H₂ near 6500 cm⁻¹ provides absolute line position accuracies of 6.0 × 10⁻⁵ cm⁻¹ (RMS) for strong, isolated transitions throughout the observed range. Fits with RMS errors <3.8 × 10⁻⁵ cm⁻¹ have been obtained for the 20013 ← 00001, 20012 ← 00001, and 20011 ← 00001 bands, RMS errors <6 × 10⁻⁵ cm⁻¹ have been obtained for the 30014 ← 00001, 30013 ← 00001, 30012 ← 00001, and 00031 ← 00001 bands, and RMS errors <5 × 10⁻⁴ cm⁻¹ for even the weakest fitted bands. This work reduces CO₂ near-infrared line position uncertainties by a factor of 10 or more compared to the 2000 HITRAN line list, which has not been modified since the comprehensive work of Rothman et al. [J. Quant. Spectrosc. Rad. Transfer 48 (1992) 537]. The new line list satisfies the line position accuracies required for the next generation of CO₂ remote sensing instruments, improves the capability of solar-viewing spectrometers to retrieve precise column CO₂ measurements, and provides a secondary frequency standard in the near-infrared.     

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 CO2 absolute line intensities from CW-CRDS and FTS measurements in the 1.6 and 2.0 μm regions

Line intensities of ¹³C¹⁶O₂ have been measured between 5851 and 6580 cm⁻¹ using CW-cavity ring down spectroscopy (CRDS) and in the 4700-5050 and 6050-6850 cm⁻¹ regions using Fourier transform spectroscopy. As a result of the high sensitivity (noise equivalent absorption α_min∼3×10⁻¹⁰ cm⁻¹) and high dynamics allowed by CW-CRDS, accurate line intensities of 2039 transitions ranging between 1.1×10⁻²⁸ and 1.3×10⁻²³ cm⁻¹/(molecule cm⁻²) were measured with an average accuracy of 4%. These transitions belong to a total of 48 bands corresponding to the ΔP=9 series of transitions. Additionally, unapodized absorption spectra of ¹³C-enriched samples have been recorded using a high-resolution Bruker IFS125HR Fourier transform spectrometer. Spectral resolutions of 0.004 cm⁻¹ (maximum optical path difference (MOPD)=225 cm) and 0.007 cm⁻¹ (MOPD=128.6 cm), and pressure×path length products in the ranges 5.2-12 and 69-450 hPa×m have been used for the lower and higher energy spectral regions, respectively. Absolute line intensities have been measured in the 2001i−00001, 3001i−00001 (i=1, 2, 3) and 00031−00001 bands. An excellent agreement was achieved for the line intensities of the 3001i−00001 (i=1, 2, 3) bands measured by both FTS and CW-CRDS. The CW-CRDS and FTS experimental intensity data together with selected intensity information from the literature have been fitted simultaneously using the effective operators approach. Two sets of effective dipole moment parameters have thus been obtained, which reproduce the observed line intensities in the 2.0 and 1.6 μm regions within experimental uncertainties.     

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).     

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-cavity ring down spectroscopy of N2O near 1.5 μm (I)

The absorption spectrum of nitrous oxide, N₂O, in natural isotopic abundance has been recorded by CW-Cavity Ring Down Spectroscopy between 6000 and 6833 cm⁻¹. The spectra were obtained at Doppler limited resolution by using a CW-CRDS spectrometer based on a series of fibered DFB lasers. The typical sensitivity of 2 × 10⁻¹⁰ cm⁻¹, allowed for the detection of lines with intensity as weak as 2 × 10⁻²⁹ cm/molecule while the minimum intensity value provided by HITRAN in the considered spectral region is 2 × 10⁻²⁵ cm/molecule. More than 6000 line positions of five isotopologues contributing to the spectra (¹⁴N₂¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁴N₂¹⁸O and ¹⁴N₂¹⁷O), were measured with a typical accuracy of 1.5 × 10⁻³ cm⁻¹ and rovibrationally assigned on the basis of their respective global effective Hamiltonian models. Highly excited rovibrational levels corresponding to J values larger than 80 could be detected for the stronger vibrational bands. The band by band analysis led to the determination of the rovibrational parameters of a total of 68 bands, 49 of them being newly reported. The rms value of the deviations of the predictions of the effective Hamiltonian models from the observed line positions is 0.010 cm⁻¹. As expected, the quality of the predictions degrades for the minor isotopologues for which important deviations up to a few wavenumbers were evidenced. Most of the bands were found unperturbed but in a few cases, local rovibrational perturbations were evidenced. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian model. In particular, interpolyad couplings were evidenced indicating that the polyad version of the effective Hamiltonian has to be extended to include Coriolis and interpolyad anharmonic interactions.     

High sensitivity CRDS of the aΔg−XΣg band of oxygen near 1.27 μm: Extended observations, quadrupole transitions, hot bands and minor isotopologues

The CW-Cavity Ring Down Spectroscopy (CW-CRDS) technique has been used to record the high sensitivity absorption spectrum of the a¹Δ_g-X³Σ_g⁻ band of oxygen near 1.27 μm. The spectra were obtained between 7640 and 7917 cm⁻¹ with “natural” oxygen and with a sample highly enriched in ¹⁸O. The absolute intensities of 376 and 643 oxygen transitions were measured in the two spectra. They include the a¹Δ_g−X³Σ_g⁻ (0-0) bands of ¹⁶O₂, ¹⁶O¹⁸O, ¹⁶O¹⁷O, ¹⁷O¹⁸O and ¹⁸O₂. The (0-0) bands of ¹⁶O₂ and ¹⁸O₂ show weak quadrupole transitions with line intensities ranging from 1×10⁻³⁰ to 1.9×10⁻²⁸ cm/molecule. They are accompanied by the a¹Δ_g−X³Σ_g⁻ (1-1) hot bands, which are reported for the first time. The line profiles of the transitions of the ¹⁶O¹⁷O and ¹⁷O¹⁸O isotopologues were observed to be broadened due to an unresolved magnetic hyperfine structure. Accurate spectroscopic parameters of the different energy levels involved in the observed bands were derived from a global fit of the observed line positions, combined with microwave and Raman measurements available in the literature.     

Fourier transform spectroscopy of N2O weak overtone transitions in the 1-2 μm region

The absorption spectrum of the natural sample of nitrous oxide has been recorded at Doppler limited resolution with a Fourier-transform spectrometer in the spectral range 5000-10 000 cm⁻¹. Ten cold bands (8Σ − Σ and 2Σ − Π), thirteen hot bands (11Π − Π, Σ − Σ, and Δ − Δ) of ¹⁴N₂¹⁶O and the 3ν₃ band of ¹⁴N¹⁵N¹⁶O have been newly detected. The uncertainty of the line position determination is estimated to be about 0.005 cm⁻¹ for unblended lines. The assignment of the spectrum has been done with the help of the prediction performed within the framework of the polyad model of effective Hamiltonian. The spectroscopic parameters G_v, B_v, D_v, H_v, and q_v have been determined for all newly detected bands. The line intensities of 13 weak bands have been measured. The uncertainty of the obtained line intensity values varies from 7 to 13%.     

Line positions and strengths of 41 bands including 10 OCS isotopologues in the 3850-4200 cm region

The present analysis substantially improves the spectroscopic characterization of near infrared OCS in a window region (3850-4200 cm⁻¹) important for atmospheric studies of Venus. Previous studies in this spectral region cataloged numerous OCS line positions, but accurate line intensities were measured for only three strong bands. In this paper, the corresponding line intensities are obtained for 41 OCS bands, including weak isotopic bands reported for the first time. The 2ν₃ (0002-0000) band is analyzed for 10 OCS isotopologues (adding ¹⁶O¹³C³⁴S, ¹⁷O¹²C³²S, ¹⁶O¹²C³⁶S, ¹⁸O¹²C³⁴S, and ¹⁶O¹³C³³S). In addition, observations of 0332-0330 of the main isotope, ¹⁶O¹²C³²S, provides accurate vibration-rotation parameters for the upper state (and the lower state, 0330 of ¹⁶O¹²C³²S). Finally, one unidentified band is seen at 3969.3 cm⁻¹; its lower state is clearly the ground state of ¹⁶O¹²C³²S. The line strengths of these seven previously unanalyzed bands plus 34 other bands of the OCS isotopologues, ¹⁶O¹²C³²S, ¹⁶O¹²C³⁴S, ¹⁶O¹³C³²S, ¹⁶O¹²C³³S, and ¹⁸O¹²C³²S, were least-squares fitted to determine strength parameters, S_v and Herman-Wallis coefficients. Finally, the intensities of 17 additional very weak bands were estimated to provide an extensive new database of OCS line parameters to support remote sensing of Venus. The integrated intensity in cm⁻¹/(molecule cm⁻²) at 296 K is 8.1×10⁻¹⁹ for the 3800-4200 cm⁻¹ region.     

Line mixing and speed dependence in CO2 at 6227.9 cm: Constrained multispectrum analysis of intensities and line shapes in the 30013 ← 00001 band

Line position, intensity and line shape parameters (Lorentz widths, pressure shifts, line mixing, speed dependence) are reported for transitions of the 30013 ← 00001 band of ¹⁶O¹²C¹⁶O (ν₀ = 6227.9 cm⁻¹). The results are determined from 26 high-resolution, high signal-to-noise ratio spectra recorded at room temperature with the McMath-Pierce Fourier transform spectrometer. To minimize the systematic errors of the retrieved parameters, we constrained the multispectrum nonlinear least squares retrieval technique to use quantum mechanical expressions for the rovibrational energies and intensities rather than retrieving the individual positions and intensities line by line. Self- and air-broadened Lorentz width and pressure-induced shift, speed dependence and line mixing (off-diagonal relaxation matrix elements) coefficients were adjusted individually. Errors were further reduced by simultaneously fitting the interfering absorptions from the weak 30012 ← 00001 band of ¹⁶O¹³C¹⁶O as well as the weak hot bands 31113 ← 01101, 32213 ← 02201, 40014 ← 10002 and 40013 ← 10001 of ¹⁶O¹²C¹⁶O in this spectral window. This study complements our previous work on line mixing and speed dependence in the 30012 ← 00001 band (ν₀ = 6347.8 cm⁻¹) [V.M. Devi, D.C. Benner, L.R. Brown, C.E. Miller, R.A. Toth, J. Mol. Spectrosc. 242 (2007) 90-117] and provides key data needed to improve atmospheric remote sensing of CO₂.