High Sensitivity CW-Cavity Ring Research Articles

Detection and analysis of three highly excited vibrational bands of 16O3 by CW-CRDS near the dissociation threshold

The present contribution is devoted to the analysis of three extremely weak A-type bands of 16O3 recorded near 7686, 7739 and 7860cm−1i.e. only a few % below the dissociation limit, D0, at about 8560cm−1. They correspond to the most excited vibration–rotation states of ozone observed so far via high-resolution absorption spectroscopy. They were detected by high sensitivity CW-cavity ring down spectroscopy with a typical noise equivalent absorption, αmin, on the order of 2×10−10cm−1 and modelled using the effective operator approach. The derived band centres and rotational constants show a very good agreement with recent theoretical predictions based on a new ab initio potential energy surface.

Three new bands of 18O16O18O by CW-CRDS between 6340 and 6800 cm−1

Three very weak bands of the 18O16O18O isotopologue of ozone have been detected by high sensitivity CW-Cavity Ring Down Spectroscopy between 6340 and 6800cm−1. They are vibrationally assigned as 2ν1+5ν3, ν1+4ν2+3ν3 and 3ν2+5ν3 and correspond to the highest frequency bands of this isotopologue detected so far. A total of 464, 318 and 194 transitions were rovibrationally assigned, respectively. The good agreement with theoretical values achieved for the derived band centres and rotational constants confirms the accuracy of the potential energy surface recently obtained via extensive ab initio calculations. A set of line intensities was measured and fitted to derive the first transition moment parameter of the three bands. The determined sets of effective Hamiltonian parameter and transition moment operators, as well as the experimental energy levels, were used to generate a complete list of 1526 transitions, provided as Supplementary materials. The calculated line-list allows generating a synthetic spectrum which reproduces satisfactorily the experimental spectrum.

High sensitivity Cavity Ring Down spectroscopy of 18O enriched carbon dioxide between 5850 and 7000 cm−1: Part III–Analysis and theoretical modeling of the 12C17O2, 16O12C17O, 17O12C18O, 16O13C17O and 17O13C18O spectra

More than 19,700 transitions belonging to 11 isotopologues of carbon dioxide have been assigned in the room temperature absorption spectrum of highly 18O enriched carbon dioxide recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990cm−1 (1.71–1.43μm). This third and last report is devoted to the analysis of the bands of five 17O containing isotopologues present at very low concentration in the studied spectra: 16O12C17O, 17O12C18O, 16O13C17O, 17O13C18O and 12C17O2 (627, 728, 637, 738 and 727 in short hand notation). On the basis of the predictions of effective Hamiltonian models, a total of 1759, 1786, 335, 273 and 551 transitions belonging to 24, 24, 5, 4 and 7 bands were rovibrationally assigned for 627, 728, 637, 738 and 727, respectively. For comparison, only five bands were previously measured in the region for the 728 species. All the identified bands belong to the ΔP=8 and 9 series of transitions, where P=2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 61 bands from a fit of the measured line positions. Two interpolyad resonance perturbations were identified.Using the newly measured line positions and those collected from the literature, the global modeling of the line positions within the effective Hamiltonian approach was performed and a new set of Hamiltonian parameters was obtained for the 17O12C18O, 16O13C17O and 17O13C18O isotopologues. For the five studied isotopologues, the effective dipole moment parameters of the ΔP=8 and 9 series were derived from a global fit of the measured line intensities. The obtained results will be used for the improvement of the quality of the line positions and intensities in the most currently used spectroscopic databases of carbon dioxide.

High sensitivity Cavity Ring Down spectroscopy of 18O enriched carbon dioxide between 5850 and 7000 cm−1: Part II—Analysis and theoretical modeling of the 12C18O2, 13C18O2 and 16O13C18O spectra

More than 19000 transitions belonging to 11 isotopologues of carbon dioxide have been assigned in the room temperature absorption spectrum of highly 18O enriched carbon dioxide recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990cm−1 (1.71–1.43μm). The line positions were determined with accuracy better than 1×10−3cm−1 while the absolute line intensities are reported with an uncertainty better than 10%. This second report is devoted to the analysis of the bands of three multiply substituted isotopologues: 12C18O2, 13C18O2 and 16O13C18O (828, 838 and 638 in short hand notation).On the basis of the predictions of effective Hamiltonian models, a total of 2870, 538 and 1375 transitions belonging to 59, 11 and 15 bands were rovibrationnally assigned for 828, 838 and 638, respectively. For comparison, only 11 bands were previously measured by Fourier Transform spectroscopy in the region, for the 828 species. All the identified bands correspond to a ΔP=9 variation of the polyad number (P=2V1+V2+3V3, where Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 81 bands from a fit of the measured line positions. A few resonance perturbations were identified. In particular, the 31113 and 51106 states of 638 belonging to different polyads (P=10 and P=11, respectively) are anharmonically coupled.Using the large set of newly measured line positions and those collected from the literature, the global modeling of the line positions within the effective Hamiltonian approach was performed and a new set of Hamiltonian parameters was obtained for each of the three considered isopotologues. Using a similar approach, the global fits of the obtained intensity values of the ΔP=9 series of transitions were used to derive the corresponding ΔP=9 effective dipole moment parameters of the three considered isotopologues. The obtained results will help to improve the quality of the spectral line parameters of the three considered minor isopotologues in the most currently used spectroscopic databases of carbon dioxide.

First detection of transitions in the second quadrupole overtone band of nitrogen near 1.44 μm by CW-CRDS with 6 × 10−13 cm−1 sensitivity

The extremely weak S(4) and S(6) electric quadrupole transitions of the 3-0 band of nitrogen have been detected by very high sensitivity CW-Cavity Ring Down spectroscopy near 6950cm−1. A noise equivalent absorption on the order of αmin∼6×10−13cm−1 was achieved by averaging several thousand 0.5cm−1 wide spectra recorded successively over several days. The studied 14N2 lines are among the weakest ever measured in the laboratory (intensity on the order of 1.5×10−31cm/molecule). The positions determined with a 0.002cm−1 uncertainty and the line intensities are compared with theoretical values included in the HITRAN2012 database.

High sensitivity Cavity Ring Down spectroscopy of 18O enriched carbon dioxide between 5850 and 7000 cm−1: I. Analysis and theoretical modeling of the 16O12C18O spectrum

The room temperature absorption spectrum of highly 18O enriched carbon dioxide has been recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990cm−1 (1.71–1.43μm). The achieved sensitivity (noise equivalent absorption αmin∼5×10−10−5×10–11cm−1) has allowed the detection of more than 19,000 transitions belonging to eleven isotopologues of carbon dioxide. This first report is devoted to the analysis of the 16O12C18O data. A total of 6452 transitions belonging to 71 bands were rovibrationnally assigned on the basis of the predictions of the effective Hamiltonian model. For comparison, only twelve 16O12C18O bands were previously measured by Fourier Transform spectroscopy in the region. Line intensities of the weakest transitions are on the order of 2×10–29cm/molecule. The studied spectral region is formed by ΔP=8, 9 and 10 series of transitions, where P=2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 69 bands from a fit of the measured line positions. A few resonance perturbations were identified. In particular, the 31112 (P=10) and 51105 (P=11) states belonging to different polyads are anharmonically coupled. The resulting intensity transfer leads to the observation of several extra lines of the 51105-01101 hot band which could be assigned.A major result of the present work is the measurement of the ΔP=8 bands of 16O12C18O near 5900cm−1 which are the main responsible of the absorption of carbon dioxide in natural isotopic abundance in the region but are absent in the current version of the CO2 spectroscopic databases (HITRAN, GEISA, and CDSD). These ΔP=8 bands may significantly impact the transmission of CO2 in the 1.70µm transparency window of importance for Venus spectra.Using the large set of newly measured line positions and those collected from the literature, the global modeling of the 16O12C18O line positions within the effective Hamiltonian approach has been performed and a new set of Hamiltonian parameters has been obtained. Using a similar approach, the global fits of the obtained intensity values of the ΔP=8, 9 and 10 series of transitions were used to derive the corresponding set of effective dipole moment parameters.The obtained results will help to improve importantly the quality of the 16O12C18O line positions and line intensities in the most currently used spectroscopic databases of carbon dioxide.

The CW-CRDS spectra of the 16O/18O isotopologues of ozone between 5930 and 6340 cm−1—Part 3: 16O18O18O and 18O16O18O

Our systematic investigation of the high sensitivity CW-Cavity Ring Down Spectra of 16O/18O ozone isotopologues at high vibrational excitation continues with the study of the 16O18O18O and 18O16O18O species. The first two papers of this series were devoted to the analysis of the same four bands of the 16O16O18O and 16O18O16O species in the 5930–6340cm−1domain. Here, after a brief reminder of relevant experiment and theory, we report the analyses of two bands of 16O18O18O, vibrationally assigned as 2ν2+5ν3 and 2ν1+2ν2+3ν3_2 and three bands of 18O16O18O, assigned to 2ν1+2ν2+3ν3_1, 5ν1+ν3 and 3ν1+ν2+3ν3.They correspond to the highest vibration excitations observed so far for the 16O18O18O and 18O16O18O isotopologues. Altogether for the two new bands of 16O18O18O, 1214 rovibrational transitions were assigned up to Jmax=29 and for the three new bands of 18O16O18O, 948 rovibrational transitions were assigned up to Jmax=27. Observed line positions were fitted with root-mean squares deviations ranging from 0.005 to 0.011cm−1, using effective Hamiltonian models accounting for dark state perturbations. The derived band centres and rotational constants are in good agreement with new theoretical calculations from the molecular potential function. The corresponding lists of 3365 lines are provided as Supplementary material.

High sensitivity CW-Cavity Ring Down Spectroscopy of N2O between 6950 and 7653 cm−1 (1.44–1.31 μm): II. Line intensities

The room temperature absorption spectra of nitrous oxide, N2O, have been recorded in the 6950–7653 cm−1 spectral region at 2 and 10Torr using a CW-CRDS spectrometer based on 24 fibered DFB lasers. The achieved sensitivity (noise equivalent absorption αmin≈5×10–11cm−1) allowed detecting lines with intensities as low as 1×10–29cm/molecule. In the preceding contribution (Lu Y, Mondelain D, Liu AW, Perevalov VI, Kassi S, Campargue A, J Quant Spectros and Radiat Transfer 2012;113:749–62), we reported the assignment of more than 7200 N2O lines in the region and the derivation of the corresponding spectroscopic parameters Gv, Bv, Dv and Hv. In the present work, more than 1300 14N216O absolute line intensities of cold and hot bands belonging to the ΔP=12, 13 and 14 series of transitions have been measured (P=2V1+V2+4V3 is the polyad number). The uncertainty of the obtained line intensity values varies from 4 to 7% for the majority of the lines. The obtained dataset extends importantly the set of measurements available in the literature, in particular for the ΔP =13 series for which previous data were very limited. The ΔP=12–14 effective dipole moment parameters were fitted to the intensity values measured in this work and available in the literature. The obtained sets of the dipole moment parameters allow reproducing the observed line intensities within their experimental uncertainties. The calculated intensities of the ΔP=12, 13 and 14 bands of 14N216O assigned by CRDS in the 6950–7653 cm−1 region are provided as supplementary material.

CRDS of water vapor at 0.1 Torr between 6886 and 7406 cm−1

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 7405.91cm−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 αmin∼2×10–11 to 2×10−10cm−1 allowing us to use a sample pressure of 0.1Torr, 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 5×10–28cm/molecule at 296K. 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 6885–7408cm−1 region.

Refinements of the WKMC empirical line lists (5852–7919 cm−1) for methane between 80 K and 296 K

During the last 4 years, empirical line lists for methane at room temperature and at 80K were constructed from spectra recorded by (i) differential absorption spectroscopy (DAS) in the high energy part of the tetradecad (5852−6195cm−1) and in the icosad (6717–7589cm−1) and (ii) high sensitivity CW-Cavity Ring Down Spectroscopy (CRDS) in the 1.58μm and 1.28μm transparency windows (6165–6750cm−1 and 7541–7919cm−1, respectively). We have recently constructed the global line lists for methane in “natural” isotopic abundance, covering the spectral region from 5854 to 7919cm−1 (Campargue A, Wang L, Kassi S, Mondelain D, Bézard B, Lellouch E, et al., An empirical line list for methane in the 1.26–1.71μm region for planetary investigations (T=80–300K). Application to Titan, Icarus 219 (2012) 110–128). These WKMC (Wang, Kassi, Mondelain, Campargue) empirical lists include about 43,000 and 46,420 lines at 80±3K and 296±3K, respectively. The “two temperature method” provided lower state energy values, Eemp, for about 24,000 transitions allowing us to account satisfactorily for the temperature dependence of the methane absorption over the considered region. The obtained lists have been already successfully applied in a large range of temperature conditions existing on Titan, Uranus, Pluto, Saturn and Jupiter.In the present contribution, we provide some improvements to our lists by using literature data to extend the set of lower state energy values and by correcting the distortion of the high Eemp values (J>10) due to the temperature gradient existing in the cryogenic cell used for the recordings. The proposed refinements are found to have an overall limited impact but they may be significant in some spectral intervals below 6500cm−1.The new version of our lists at 80K and 296K is provided as Supplementary Material: the WKMC@80K+ and WKMC@296K lists are adapted for planetary and atmospheric applications, respectively. The WKMC@80K+ list is made applicable over a wider range of temperatures and shows satisfactory extrapolation capabilities up to room temperature. It was obtained by transferring to the 80K list the 27,580 single lines present only in the 296K list, with corresponding lower state energy values chosen to make them below the detectivity limit at 80K.In the discussion, the different line lists and databases available for methane in the near infrared are compared and some suggestions are given.

The absorption spectrum of D2: Ultrasensitive cavity ring down spectroscopy of the (2–0) band near 1.7 μm and accurate ab initio line list up to 24 000 cm−1

Eleven very weak electric quadrupole transitions Q(2), Q(1), S(0)-S(8) of the first overtone band of D(2) have been measured by very high sensitivity CW-cavity ring down spectroscopy (CRDS) between 5850 and 6720 cm(-1). The noise equivalent absorption of the recordings is on the order of α(min) ≈ 3 × 10(-11) cm(-1). By averaging a high number of spectra, the noise level was lowered to α(min) ≈ 4 × 10(-12) cm(-1) in order to detect the S(8) transition which is among the weakest transitions ever detected in laboratory experiments (line intensity on the order of 1.8 × 10(-31) cm/molecule at 296 K). A Galatry profile was used to reproduce the measured line shape and derive the line strengths. The pressure shift and position at zero pressure limit were determined from recordings with pressures ranging between 10 and 750 Torr. A highly accurate theoretical line list was constructed for pure D(2) at 296 K. The intensity threshold was fixed to a value of 1 × 10(-34) cm/molecule at 296 K. The obtained line list is provided as supplementary material. It extends up to 24,000 cm(-1) and includes 201 transitions belonging to ten v-0 cold bands (v = 0-9) and three v-1 hot bands (v = 1-3). The energy levels include the relativistic and quantum electrodynamic corrections as well as the effects of the finite nuclear mass. The quadrupole transition moments are calculated using highly accurate adiabatic wave functions. The CRDS line positions and intensities of the first overtone band are compared to the corresponding calculated values and to previous measurements of the S(0)-S(3) lines. The agreement between the CRDS and theoretical results is found within the claimed experimental uncertainties (on the order of 1 × 10(-3) cm(-1) and 2% for the positions and intensities, respectively) while the previous S(0)-S(3) measurements showed important deviations for the line intensities.

High sensitivity CW-Cavity Ring Down Spectroscopy of N2O between 6950 and 7653 cm−1 (1.44–1.31 μm): I. Line positions

The absorption spectrum of nitrous oxide, N2O, has been recorded by CW-Cavity Ring Down Spectroscopy between 6950 and 7653cm−1. The spectra were obtained at Doppler limited resolution using a CW-CRDS spectrometer based on a series of fibered DFB laser diodes. The typical noise equivalent absorption, in the order of αmin≈1×10−10cm−1, allowed for the detection of lines with intensity as small as 1×10–29cm/molecule.The positions of 7203 lines of four isotopologues (14N216O, 14N15N16O, 15N14N16O and 14N218O) were measured with a typical accuracy of 1.0×10−3cm−1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian models developed for each isotopologue. The band by band analysis allowed for the determination of the rovibrational parameters of more than 95 bands, most of them being newly reported while new rotational transitions are measured for the others. The measured line positions of the main isotopologue are found to be in good agreement with the predictions of the effective Hamiltonian model but a few deviations up to 0.20cm−1 are observed. Local rovibrational perturbations were evidenced for several bands. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian models.

Detection and analysis of four new bands in CRDS 16O3 spectra between 7300 and 7600 cm−1

The absorption spectrum of the 16O3 isotopologue of ozone was recorded in the 7000–7920cm−1 region by using high sensitivity CW-Cavity Ring Down Spectroscopy (αmin∼10−10cm−1). This report is devoted to the analysis of the 7300–7600cm−1 region dominated by four A-type bands: 6ν1+ν3 centred around 7395cm−1, 3ν1+5ν2+ν3 and 2ν1+4ν2+3ν3 lying in the 7450cm−1 region and 5ν1+2ν2+ν3 centred around 7579cm−1. 213 transitions of the 6ν1+ν3 band were assigned and the corresponding line positions were modeled using an effective Hamiltonian including a Coriolis resonance interaction between the (601) upper state and a A-type dark state. The two very close 3ν1+5ν2+ν3 and 2ν1+4ν2+3ν3 bands were analysed using a similar effective Hamiltonian scheme involving the anharmonic resonance coupling between the (351) and (243) states. For these two bands, 304 transitions were assigned. The modelling also includes a first Coriolis resonance interaction between the (351) bright state and the (530) dark state, and a second one between the (243) bright state and the (144) dark state. In the 7579cm−1 region, 205 transitions of the 5ν1+2ν2+ν3 band were assigned and modelled taking into account the Coriolis resonance interactions between the (521) upper state and the (700), (342) and (280) dark states.The dipole transition moment parameters of the four analysed bands were determined by a least-squares fit to the measured line intensities. For the studied band systems, the effective Hamiltonian and transition moment operator parameters were used to generate line lists provided as Supplementary Materials.

The absorption spectrum of H2: CRDS measurements of the (2-0) band, review of the literature data and accurate ab initio line list up to 35 000 cm−1

Five very weak transitions-O(2), O(3), O(4), O(5) and Q(5)-of the first overtone band of H(2) are measured by very high sensitivity CW-Cavity Ring Down Spectroscopy (CRDS) between 6900 and 7920 cm(-1). The noise equivalent absorption of the recordings is on the order of α(min)≈ 5 × 10(-11) cm(-1) allowing for the detection of the O(5) transition with an intensity of 1.1 × 10(-30) cm per molecule, the smallest intensity value measured so far for an H(2) absorption line. A Galatry profile was used to reproduce the measured line shape and derive the line strengths. The pressure shift of the O(2) and O(3) lines was accurately determined from a series of recordings with pressure ranging between 10 and 700 Torr. From an exhaustive review of the literature data, the list of H(2) absorption lines detected so far has been constructed. It includes a total of 39 transitions ranging from the S(0) pure rotational line near 354 cm(-1) up to the S(1) transition of the (5-0) band near 18,908 cm(-1). These experimental values are compared to a highly accurate theoretical line list constructed for pure H(2) at 296 K (0-35,000 cm(-1), intensity cut off of 1 × 10(-34) cm per molecule). The energy levels and transition moments were computed from high level quantum mechanics calculations. The overall agreement between the theoretical and experimental values is found to be very good for the line positions. Some deviations for the intensities of the high overtone bands (V > 2) are discussed in relation with possible pressure effects affecting the retrieved intensity values. We conclude that the hydrogen molecule is probably a unique case in rovibrational spectroscopy for which first principles theory can provide accurate spectroscopic parameters at the level of the performances of the state of the art experimental techniques.

First high-resolution analysis of the 5ν3 band of nitrogen dioxide near 1.3 μm

The first high-resolution absorption spectrum of the 5ν3 band of the 14N16O2 molecule at 7766.071cm−1 was recorded by high sensitivity CW-Cavity Ring Down Spectroscopy between 7674 and 7795cm−1. The noise equivalent absorption of the recordings was αmin≈1×10−10cm−1. The assignments involve energy levels of the (0,0,5) vibrational state with rotational quantum numbers up to Ka=9 and N=47. The set of the spin–rotation energy levels were reproduced within their experimental uncertainty using a theoretical model, which takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,5) vibrational state and those of the (0,2,4) dark state together with the electron spin–rotation resonances within the (0,0,5) and (0,2,4) states. Precise values were determined for the (0,0,5) vibrational energy rotational, spin-rotational constants and for the (0,2,4)⇔(0,0,5) coupling constants. In addition the (0,2,4) rotational and spin-rotational constants were estimated. Using these parameters and the value of the transition dipole moment operator determined from a fit of a selection of experimental line intensities, the synthetic spectrum of the 5ν3 band was generated and is provided as Supplementary material.

Detection and analysis of new bands of 16O 3 by CRDS between 6500 and 7300 cm −1

The absorption spectrum of the 16O 3 isotopologue of ozone has been recorded in the 7000–7920 cm −1 region by high sensitivity CW-Cavity Ring Down Spectroscopy. This report is devoted to the analyses of the 7065–7300 cm −1 region dominated by the ν 1 + 2 ν 2 + 5 ν 3 and ν 1 + 5 ν 2 + 3 ν 3 A-type bands at 7130.8 and 7286.8 cm −1 respectively. 289 transitions were assigned to the ν 1 + 2 ν 2 + 5 ν 3 band. The corresponding line positions were modeled with an effective Hamiltonian involving Coriolis resonance interactions between the (1 2 5) upper state and the (4 4 0), (0 2 6) and (6 1 0) dark states, and an anharmonic resonance interaction with the (2 0 5) state. The very strong interaction (up to 50% mixing of the wavefunctions) between the (1 2 5) and (6 1 0) states leads to the observation of two extra lines of the 6 ν 1 + ν 2 band due to a resonance intensity transfer. 213 transitions of the ν 1 + 5 ν 2 + 3 ν 3 band were assigned and modeled taking into account a Coriolis resonance interaction with the (3 6 0) state. We take the opportunity of the present work to report the analysis of the very weak 4 ν 2 + 4 ν 3 B-type band at 6506.1 cm −1 which was assigned from previously recorded CRDS spectra. 286 transitions were modeled using the effective Hamiltonian approach. The dipole transition moment parameters of the three analyzed bands were determined by a least-squares fit to the measured line intensities. For the three studied band systems, the effective Hamiltonian and transition moment operator parameters were used to generate line lists provided as Supplementary Materials.

The absorption spectrum of water in the 1.25 μm transparency window (7408–7920 cm −1)

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded between 7408 and 7920 cm −1 by high sensitivity cw-cavity ring down spectroscopy (CW-CRDS). This region covers the low energy part of the 1.25 μm transparency window and corresponds to weak water absorption of the first hexad of interacting vibrational bands. The achieved sensitivity – on the order of α min ∼ 2 × 10 −10 cm −1 – has allowed one to newly measure 2028 weak transitions with intensities down to 2 × 10 −29 cm/molecule at 296 K i.e. more than two orders of magnitude lower than previous observations. Three hundred and fourty-one new and corrected energy levels belonging to 26 vibrational states of H 2 16O, H 2 18O, H 2 17O, and HD 16O could be determined from the vibration–rotation analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the studied region by Fourier Transform Spectroscopy and existing databases have been critically evaluated. The most complete list for water in the region is provided as Supplementary Material.

High sensitivity CW-Cavity Ring Down Spectroscopy of N 2O near 1.28 μm

The absorption spectrum of nitrous oxide, N 2O, in normal isotopic abundance has been recorded by CW-Cavity Ring Down Spectroscopy between 7647 and 7918 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 noise equivalent absorption on the order of α min ≈ 1 × 10 −10 cm −1, allowed for the detection of lines with intensity as weak as 2 × 10 −29 cm/molecule. The positions of 2272 lines of five isotopologues ( 14N 2 16O, 15N 14N 16O, 14N 15N 16O, 14N 2 18O and 14N 2 17O), were measured with a typical accuracy of 1.0 × 10 −3 cm −1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian models respective to each isotopologue. The band by band analysis allowed for the determination of the rovibrational parameters of a total of 30 bands, 19 of them being newly reported while new rotational transitions are measured for the others. The maximum deviation of the predictions of the effective Hamiltonian models is 0.18 cm −1 for the line positions of the main isotopologue and up to 1.3 cm −1 for the 14N 2 18O species. Local rovibrational perturbations were evidenced for three bands of 14N 2 16O and the ν 1 + 3 ν 3 band of 14N 2 17O. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian models.

The [formula omitted] band of 16O 17O, 17O 18O and 17O 2 by high sensitivity CRDS near 1.27 μm

The very weak a 1 Δ g − X 3 Σ g − system of the three 17O isotopologues of oxygen – 16O 17O, 17O 18O and 17O 2 – was studied by high sensitivity CW-Cavity Ring Down Spectroscopy. The spectra of a 17O highly enriched sample were recorded at room temperature between 7640 and 7917 cm −1 and at liquid nitrogen temperature in the 7876–7893 cm −1 region. The magnetic dipole (0–0) band was observed for all three 17O isotopologues. At liquid nitrogen temperature, some of the transitions were observed with partially resolved hyperfine splitting due to the 17O nuclear spin. The electric quadrupole (0–0) band and the (1–1) hot band were also observed for the 16O 17O and 17O 2 species. The rotational and hyperfine spectroscopic parameters of the X 3 Σ g − and a 1Δ g states of the three studied isotopologues were derived from a global fit of the measured line positions and microwave and Raman measurements available in the literature. The spectroscopic constants of the a 1Δ g ( v=0, 1) states of 17O 2 are reported for the first time.

First identification of the [formula omitted] electric quadrupole transitions of oxygen in solar and laboratory spectra

Electric quadrupole transitions in the a 1 Δ g – X 3 Σ g − band of 16O 2 near 1.27 μm are reported for the first time. They were first detected in atmospheric solar spectra acquired with a ground-based Fourier transform spectrometer (FTS) in Park Falls, WI. Subsequently high-sensitivity CW—cavity ring down spectroscopy (CW-CRDS) experiments were carried out at Grenoble University in the 7717–7917 cm −1 region in order to provide quantitative intensity information for the electric quadrupole transitions. Measured intensities were used as input data for the calculation of the complete list of electric quadrupole transitions with Δ J=±2, ±1 and 0. The calculation was carried out for the intermediate coupling case and assuming that these transitions are possible only through mixing of the Ω=0 component of the ground electronic state and b 1 Σ g + state induced by spin–orbit coupling. The calculated line list agrees well with experimental measurements and was used to improve the residuals of the fitted solar atmospheric spectrum. Emission probability for the electric quadrupole band was determined to be (1.02±0.10)×10 −6 s −1.