High Sensitivity CW-Cavity Ring Research Articles

High sensitivity CW-Cavity Ring Down Spectroscopy of five 13CO 2 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 CO 2 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 13C 16O 2, 16O 13C 17O, 16O 13C 18O, 17O 13C 18O and 13C 18O 2 isotopologues. For comparison, only 104 line positions of 13C 16O 2 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 13C 16O 2 species. The measured line positions of 13C 16O 2 and 16O 13C 18O 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 13C 16O 2, 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 16O 13C 17O and 16O 13C 18O. 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.

High sensitivity CW-cavity ring down spectroscopy of 12CO 2 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 12CO 2 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 12C 16O 2 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 ( 12C 16O 2, 13C 16O 2, 16O 12C 18O and 16O 12C 17O) 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 12C 16O 2 bands together with selected intensity information available in the literature for nine bands have been fitted simultaneously using the effective operators approach. The Δ P=11 set of the 12C 16O 2 effective dipole moment parameters has been refined leading to a much better agreement with the measured intensity values. In addition, the Δ P=10 effective dipole moment parameters of the 16O 12C 18O minor isotopologue were determined for the first time. The obtained results will help to improve the carbon dioxide spectroscopic databank (CDSD).

High sensitivity CW-cavity ring down spectroscopy of 12CO 2 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 CO 2 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 1 2C 16O 2, 1 6O 1 2C 1 7O and 1 6O 1 2C 1 8O 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 1 2C 16O 2, 1 6O 1 2C 1 7O and 1 6O 1 2C 1 8O 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 1 2C 16O 2 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 1 6O 1 2C 1 7O and 1 6O 1 2C 1 8O 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.

CW-Cavity Ring Down spectroscopy of 18O 3. Part 1: Experiment and analysis of the 6200–6400 cm −1 spectral region

The absorption spectrum of the 18O 3 isotopologue of ozone has been recorded in the 6200–6400 cm −1 region by high sensitivity CW-Cavity Ring Down Spectroscopy. The spectrum is dominated by the 2ν 1 + 5ν 3 and 2ν 1 + 3ν 2 + 3ν 3 bands at 6270.6 and 6392.2 cm −1, respectively which were treated independently. The rovibrational analysis of the 2ν 1 + 5ν 3 band has evidenced that the (2 0 5) upper state is perturbed by Coriolis resonance interactions with the (0 1 6), (3 0 4) and (3 5 0) states. A total of 659, 89, 131 and 5 transitions were assigned to the 2ν 1 + 5ν 3, ν 2 + 6ν 3, 3ν 1 + 4ν 3 and 3ν 1 + 5ν 2 bands, respectively. In the case of the 2ν 1 + 3ν 2 + 3ν 3 band, 344 transitions were assigned. Some of them were found perturbed by a Coriolis interaction of the (2 3 3) state with the (5 2 0) state. Overall, 681 energy levels were derived from the analysis of the 2ν 1 + 5ν 3 and 2ν 1 + 3ν 2 + 3ν 3 band systems. In both cases, a suitable effective Hamiltonian was elaborated, allowing accounting satisfactorily for the retrieved rovibrational energy levels. In addition, dipole transition moment parameters were determined by a least-squares fit to the measured line intensities. The effective Hamiltonian and transition moment operator parameters were used to generate a list of 1619 transitions given as Supplementary material.

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高灵敏度调谐式连续波腔衰荡光谱技术

High sensitivity CW-cavity ring down spectroscopy of N 2O near 1.5 μm (III)

We present the third part of the investigation of the high sensitivity absorption spectrum of nitrous oxide by CW-Cavity Ring Down Spectroscopy near 1.5 μm. In the two first contributions (A. Liu, et al., J. Mol. Spectrosc. 244 (2007) 33–47 and A. Liu, et al., J. Mol. Spectrosc. 244 (2007) 48–62) devoted to the 5905–6833 cm −1 region, more than 9000 line positions of five isotopologues ( 14N 2 16O, 15N 14N 16O, 14N 15N 16O, 14N 2 17O and 14N 2 18O), were rovibrationally assigned to a total of 115 bands, most of them being newly detected. The achieved sensitivity ( α min∼3 × 10 −10 cm −1) allowed for the detection of lines with intensity weaker than 2 × 10 −29 cm/molecule. In this contribution, the investigated region was extended up to 7066 cm −1. The analysis based on the predictions of the effective Hamiltonian model has allowed assigning about 1500 transitions to 17, 1, 2 and 1 bands of the 14N 2 16O, 14N 15N 16O, 15N 14N 16O and 14N 2 18O isotopologues, respectively. Eleven of these 21 bands are newly reported, while the observations of the transitions are extended to higher J values for most of the others. The band by band analysis has allowed reproducing the measured line positions within the experimental uncertainty (about 1 × 10 −3 cm −1) and determining the corresponding spectroscopic parameters. A detailed analysis of the rovibrational perturbations affecting three bands of 14N 2 16O is presented.

High sensitivity CW-CRDS spectroscopy of 12C 16O 2, 16O 12C 17O and 16O 12C 18O between 5851 and 7045 cm −1: 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 12C 16O 2, 16O 12C 17O and 16O 12C 18O 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 16O 12C 18O 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.

Comment on “Spectroscopic database of CO 2 line parameters: 4300–7000 cm –1”

The “Spectroscopic database of CO 2 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 (CO 2) 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 13CO 2 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 ( 13C 16O 2, 16O 13C 18O and 16O 13C 17O) but the conclusions should apply to the other isotopologues in particular 12C 16O 2 and to the full spectral range of the database. Alternatively, the global effective operators models for CO 2 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 CO 2 isotopologues, constitutes an interesting alternative for the most accurate and complete CO 2 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 ring down spectroscopy of CH 4 in the 1.55 μm transparency window

The high resolution absorption spectrum of methane has been recorded at room temperature by high sensitivity CW-cavity ring down spectroscopy between 1.50 and 1.60 μm (6250–6680 cm −1). This spectral region has a low opacity and is then of particular interest for the spectral analysis of the outer planets and Titan. The recordings were performed with a sensitivity corresponding to a noise equivalent absorption of α min ∼ 5 × 10 −10 cm −1 and allowed for the detection of lines with an intensity smaller than 10 −28 cm/molecule far beyond the weakest lines provided by the HITRAN database. The spectrum exhibits a highly complex and congested structure with a kind of ‘fractal’ character and a density of transitions of a few tens per cm −1. The impact of the weak newly observed transitions on the total absorption in the region is discussed.

CW-cavity ring down spectroscopy of the ozone molecule in the 6220–6400 cm −1 region

The absorption spectrum of ozone, 16O 3, has been recorded in the 6220–6400 cm −1 region by high sensitivity CW-cavity ring down spectroscopy ( α min ∼ 3 × 10 −10 cm −1). 1836 rovibrational transitions have been assigned to the 2 ν 2 + 5 ν 3, 5 ν 1 + ν 3 and 2 ν 1 + 2 ν 2 + 3 ν 3 A-type bands centred at 6305, 6355 and 6387 cm −1, respectively. In addition, 99 lines of the very weak ν 1 + 2 ν 2 + 4 ν 3 and 4 ν 1 + 3 ν 2 B-type bands are identified. The modeling of the observed spectrum in the effective Hamiltonian approach was particularly laborious and complex as several rovibrational interactions of both Coriolis and anaharmonic type were found to be of importance, in particular for the (124) vibrational state. Nevertheless, it has finally been possible to fit the 990 experimentally determined energy levels with an rms deviation of 8.29 × 10 −3 cm −1 and to derive the transition moment parameters allowing a satisfactory reproduction of the observed intensities. As the differences in positions between the final calculations and observations are still larger than the experimental accuracy, we provide the list of all energy levels derived from the observation, in addition to their differences with the calculated ones. These experimental energy levels, with the transition moment parameters were used to generate a line-list of 2451 transitions, reproducing the observed spectrum. This list is given as Supplementary Material.

The ν1 + 3 ν2 + 3 ν3 and 4 ν1 + ν2 + ν3 bands of ozone by CW-cavity ring down spectroscopy between 5900 and 5960 cm −1

The absorption spectrum of ozone, 16O 3, has been recorded in the 5903–5960 cm −1 region by high sensitivity CW-cavity ring down spectroscopy ( α min ∼ 5 × 10 −10 cm −1). The ν 1 + 3 ν 2 + 3 ν 3 and 4 ν 1 + ν 2 + ν 3 A-type bands centred at 5919.15 and 5947.07 cm −1 were newly observed. A set of 173 and 168 energy levels could be experimentally determined for the (1 3 3) and (4 1 1) states, respectively. Except for a few K a = 5 levels of the (4 1 1) state, the rotational structure of the two states was found mostly unperturbed. The spectroscopic parameters were determined from a fit of the corresponding line positions by considering the (1 3 3) and (4 1 1) states as isolated. The determined effective Hamiltonian and transition moment operators were used to generate a list of 785 transitions given as Supplementary Material.

High sensitivity CW-Cavity Ring Down Spectroscopy of N 2O near 1.5 μm (II)

We present the second part of the investigation of the high sensitivity absorption spectrum of nitrous oxide by CW-Cavity Ring Down Spectroscopy near 1.5 μm. In a first paper [A.W. Liu, S. Kassi, P. Malara, D. Romanini, V.I. Perevalov, S.A. Tashkun, S.M. Hu, A. Campargue, J. Mol. Spectrosc. 244 (2007) 33–47] devoted to the 6000–6833 cm −1 region, more than 6000 line positions of five isotopologues ( 14N 2 16O, 15N 14N 16O, 14N 15N 16O, 14N 2 17O, and 14N 2 18O), were rovibrationally assigned to a total of 68 bands. The achieved noise equivalent absorption ( α min ∼ 2 × 10 −10 cm −1) allowed for the detection of lines with intensity weaker than 2 × 10 −29 cm/molecule. In this contribution, the investigated region was extended down to 5905 cm −1 and additional recordings allowed accessing small spectral sections uncovered in our preceding recordings. A deeper analysis based on the predictions of the effective Hamiltonian model has allowed assigning a total of 3149 transitions and lowering the percentage of lines left unassigned from 51% to 28%. It led to the analysis of 35, 6, 7, and 6 bands for the 14N 2 16O, 15N 14N 16O, 14N 15N 16O, and 14N 2 18O isotopologues, respectively. Forty-two of these 54 bands are newly observed, while the rotational analysis of the twelve others is significantly extended and improved. Most of the bands were found unperturbed and their line positions could be reproduced within the experimental uncertainty (about 1 × 10 −3 cm −1). The corresponding spectroscopic parameters are reported. Local rovibrational perturbations induced by either intrapolyad or interpolyad couplings were found to affect five hot bands of 14N 2 16O. Their detailed analysis is presented.

CW-Cavity Ring Down Spectroscopy of the ozone molecule in the 5980–6220 cm −1 region

The absorption spectrum of ozone, 16O 3, has been recorded in the 5980–6220 cm −1 region by high sensitivity CW-Cavity Ring Down Spectroscopy ( α min ∼ 3 × 10 −10 cm −1). This study extends a first investigation with the same experimental set-up limited to the 6030–6090 cm −1 spectral region [M.-R. De Backer-Barilly, A. Barbe, Vl.G. Tyuterev, D. Romanini, B. Moeskops, A. Campargue, J. Mol. Struct. 780–781 (2006) 225–233] where the analysis of two A-type bands was reported, using FTS spectra for complementary information. The spectral extension of the recordings allows not only to enlarge considerably the observed transitions of these two bands, but more importantly, to assign four new bands: the 3 ν 2 + 4 ν 3,5 ν 1 + ν 2 and ν 1 + 2 ν 2 + 4 ν 3 B-type bands which were considered as dark in our previous report and the 3 ν 1 + 3 ν 2 + ν 3 A-type band. The high mixing of the observed states approaching the dissociation limit, leads to the breakdown of the polyad structure and ambiguities in the vibrational labelling which are discussed. Finally, 1789 transitions were assigned, and a suitable Hamiltonian model allows reproducing correctly the observations for five of the six observed bands. The list of 1004 experimentally determined energy levels is provided. The determined effective Hamiltonian and transition moment operators were used to generate a list of 5338 transitions given as Supplementary Material. It is interesting to note that the d 5 parameter of the effective transition moment is of great importance to account for the observed intensities of the B-type bands.

High sensitivity CW-cavity ring down spectroscopy of N 2O near 1.5 μm (I)

The absorption spectrum of nitrous oxide, N 2O, 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 ( 14N 2 16O, 15N 14N 16O, 14N 15N 16O, 14N 2 18O and 14N 2 17O), 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.

Very high sensitivity CW-cavity ring down spectroscopy: Application to the [formula omitted] O 2 band near 1.58 μm

A few absorption lines of the Q Q branch of the a 1 Δ g ( 0 ) – X 3 Σ g - ( 1 ) hot band of pure O 2 have been detected near 1.58 μm by CW-cavity ring down spectroscopy based on a fibred DFB laser. A sensitivity of the order of 2 × 10 −11 cm −1 has been achieved by averaging a large number of spectra, allowing for the measurement of line intensities as weak as 5 × 10 −31 cm/molecule. The integrated band intensity is estimated to be S 01 = 4.5(7) × 10 −29 cm/molecule which differs by a factor of about 6 from the value provided by the HITRAN database. Our intensity value is supported by a significantly better agreement with the value deduced from the intensity of the a 1 Δ g ( 0 ) – X 3 Σ g - ( 0 ) cold band and the respective Franck–Condon factors.

High sensitivity CW-cavity ring down spectroscopy of water in the region of the 1.5 μm atmospheric window

The absorption spectrum of natural water vapour around 1.5 μm has been recorded with a typical sensitivity of 5 × 10 −10 cm −1 by using a CW-cavity ring down spectroscopy set up based on fibred DFB lasers. A series of 31 DFB lasers has allowed a full coverage of the 6130.8–6748.5 cm −1 (1.63–1.48 μm) region corresponding to the H transparency band of the atmosphere. The line parameters (wavenumber and intensity) of a total of 5190 lines, including 4247 lines of water vapor, were derived by a one by one fit of the lines to a Voigt profile. Different isotopologues of water (H 2 16O, H 2 18O, H 2 17O, and HD 16O) present in natural abundance in the sample contribute to the spectrum. For the main isotopologue, H 2 16O, 2130 lines were measured with line intensities as weak as 10 −29 cm/molecule while only 926 lines (including a proportion of 30% inaccurate calculated lines) with a minimum intensity of 3 × 10 −27 cm/molecule are provided by the HITRAN and GEISA databases. Our comparison in the whole 5750–7965 cm −1 region, has also evidenced that an error in the process of conversion of the intensity units from cm −2/atm to cm −1/(molecule × cm −2) at 296 K, has led to H 2 16O line intensities values listed in the HITRAN-2000 database, systematically 8 % below the original FTS values. The rovibrational assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge with a subsequent refinement and validation using the Ritz combination principle together with all previously measured water transitions relevant to this study. This procedure allowed determining 172, 139, 71, and 115 new energy levels for the H 2 16O, H 2 18O, H 2 17O, and HD 16O isotopologues, respectively. The results are compared with the available databases and discussed in regard of previous investigations by Fourier transform spectroscopy. The spectrum analysis has showed that most of the transitions which cannot be assigned to water are very weak and are due to impurities such as carbon dioxide and ammonia, leaving only about 3% of the observed transitions unassigned. The interest of a detailed knowledge of water absorption for trace detectors developed in the 1.5 μm range is underlined: for instance HDO contributes significantly to the considered spectrum while no HDO line parameters are provided by the HITRAN database.