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The first accurate and complete theoretical room-temperature rotationally resolved spectra in the range 300–3000 cm−1 are reported for the three most abundant isotopologues (32SF6, 33SF6 and 34SF6) of the sulfur hexafluoride molecule. The literature reports that SF6 is widely used as a prototype molecule for studying the multi-photon excitation processes with powerful lasers in the infrared range. On the other hand, SF6 is an important greenhouse molecule with a very long lifetime in the atmosphere. Because of relatively low vibrational frequencies, the hot bands of this molecule contribute significantly to the absorption infrared spectra even at room temperature. This makes the calculation of complete rovibrational line lists required for fully converged opacity modeling extremely demanding. In order to reduce the computational costs, symmetry was exploited at all stages of the first global variational nuclear motion calculations by means of irreducible tensor operators. More than 2600 new vibrational band centers were predicted using our empirically refined ab initio potential energy surface. Highly excited rotational states were calculated up to J = 121, resulting in 6 billion transitions computed from an ab initio dipole moment surface and distributed over more than 500 cold and hot bands. The final line lists are made available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru). For the first time, the major (ro)vibrational band structures in the wavenumber range corresponding to the strongest absorption in the infra-red are completely elucidated for a seven-atom molecule, providing excellent agreement with the observed spectral patterns. It is shown that the obtained results are more complete than all available line lists, permitting reliable modelling of the temperature dependence of the molecular opacity.

The Fourier transform spectrum of CF4 in the 1600–1800 cm − 1 was recorded in Reims by using a White-type multi-pass cell to provide a path length of 8.262 m. In the present work, all spectrum analyses and fits were realized using the MIRS software based on tetrahedral tensorial formalism. By combining non-empirical contact transformation Hamiltonians for line positions and ab initio ro-vibrational normal-mode predictions for line intensities, we are able to achieve a simultaneous fit of effective Hamiltonian and dipole moment parameters of several cold and hot bands of CF4. Hamiltonian operator was expanded up to the sixth order for the ground state and for the { ν 2 + 2 ν 4 , ν 2 + ν 3 , 4 ν 2 , ν 1 + 2 ν 2 , 2 ν 1 } pentad. 1831 line positions were fitted to RMS of 1.5X10−3 cm−1. The standard deviation for line intensities for the cold bands { ν 2 + 2 ν 4 , ν 2 + ν 3 , 4 ν 2 , ν 1 + 2 ν 2 , 2 ν 1 } is of 1.1% and of 8% and 5% for the hot band transitions { 2 ν 2 + 2 ν 4 − ν 2 , 2 ν 2 + ν 3 − ν 2 } and { ν 2 + 3 ν 4 − ν 4 , ν 2 + ν 3 + ν 4 − ν 4 } , respectively.

International audience; Vibrational energy levels of H 2 CO are reported using global variational nuclear motion calculations from new ab initio and empirically optimized full 6-dimensional ab initio potential energy surfaces in ground electronic state of the formaldehyde molecule. Ab initio calculations were carried out using extended electronic structure coupled-cluster calculations accounting for dynamic electron correlations including triple and quadruple excitations as well as relativistic and diagonal Born-Oppenheimer corrections. Variational nuclear motion calculations are compared in different set of coordinates with exact kinetic energy operator and in normal coordinates with Watson-Eckart kinetic energy operator. Our best ab initio potential energy surface including the above mentioned contributions provides the RMS (obs.-calc.) errors of 0.25 cm-1 for fifteen vibrational band centers without empirically adjusted parameters. The average error drops down to 0.08 cm-1 for an empirically optimized potential energy function with six adjusted parameters corresponding to quadratic force field terms. The estimation of the accuracy for the calculated vibrational levels in an extended range up to 4500 cm-1 shows that the set of ab initio vibrational levels could be more consistent than experimental levels obtained from earlier studies of low resolution spectra. The comparison of the calculated and experimental vibrational energy levels of the D 2 CO isotopologue is also reported.

Four spectra of normal samples of CH4 in the 4300–4600 cm−1 region were recorded by using a Fourier transform spectrometer in Reims, France at long paths (202 m, 602 m, 1604 m, and 1804 m) and different pressures. Additional spectra of 12CH4 covering the same region were obtained at 80–123 K, and 93 m path length at SOLEIL Synchrotron in Paris for different pressures and were used to measure low-J lines. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures and analyzed using effective Hamiltonian and effective dipole transition moment models. A new measured line list contains positions and intensities for 14,151 absorption features. Quantum assignments were made for more than 10,304 transitions of 12CH4, which represent ∼99% of the integrated line intensity observed in this region. Some 1699 hot band transitions for (Dyad – Tetradecad) system were assigned. The resulting list of lines is significantly more accurate than previous empirical compilations. Positions of 8605 cold band transitions for (GS – Octad) system were fitted with an RMS standard deviation of 0.0014 cm−1. The sum of observed intensities between 4300 and 4600 cm−1 fell within 8% of the predicted value from ab initio variational calculations reported in the TheoReTS database ( http://theorets.univ-reims.fr ; http://theorets.tsu.ru ).

In this paper, we report a series of transformations for the construction of a Hamiltonian model for nonrigid polyatomic molecules in the framework of the Hougen-Bunker-Johns formalism (HBJ). This model is expressed in normal mode coordinates for small vibrations and in a specific coordinate ρ to describe the large amplitude motion. For the first time, a general procedure linking the "true" curvilinear coordinates to ρ is proposed, allowing the expression of the potential energy part in the same coordinate representation as the kinetic energy operator, whatever the number of atoms. A Lie group-based method is also proposed for the derivation of the reference configuration in the internal axis system. This work opens new perspectives for future high-resolution spectroscopy studies of nonrigid, medium-sized molecules using HBJ-type Hamiltonians. Illustrative examples and computation of vibrational energy levels on semirigid and nonrigid molecules are given to validate this method.

Three spectra of normal samples of CH4 in the 8850–9180 cm−1 region were recorded at temperatures 296 K, 254 K, 208 K by using a Fourier transform spectrometer in Tomsk with the cell path of 2.2 m. Additional spectra of 12CH4 covering the same spectral range were obtained at 108 K with the cell path of 0.2 m. The lower energy levels were corrected for 1029 lines available in the HITRAN [1] database in this range. Additionally, 275 new quantum assignments were added using ab initio variational calculations combined with the spectra analyses based on effective Hamiltonian and effective dipole transition moment fits. Simulations of observed spectra show that new line list is much more accurate for lower temperatures than the previous compilation included in HITRAN-2016. Finally, the lower state energies are provided for 1304 transitions that represents ∼66% of the integrated line intensity observed in this region at 296 K. The sum of observed intensities between 8850 and 9180 cm−1 agree within 7% to the predicted value of ab initio variational calculations reported in the TheoReTS database (http://theorets.univ-reims.fr; http://theorets.tsu.ru).

The spectrum of methane is very important for the analysis and modeling of Titan’s atmosphere but its insufficient knowledge in the near infrared, with the absence of reliable absorption coefficients, is an important limitation. In order to help the astronomer community for analyzing high-quality spectra, we report in the present work the first accurate theoretical methane line lists (T = 50–350 K) of 12 CH 4 and 13 CH 4 up to 13400 cm − 1 ( > 0.75 µm). These lists are built from extensive variational calculations using our recent ab initio potential and dipole moment surfaces and will be freely accessible via the TheoReTS information system ( http://theorets.univ-reims.fr , http://theorets.tsu.ru ). Validation of these lists is presented throughout the present paper. For the sample of lines where upper energies were available from published analyses of experimental laboratory 12 CH 4 spectra, small empirical corrections in positions were introduced that could be useful for future high-resolution applications. We finally apply the TheoRetS line list to model Titan spectra as observed by VIMS and by DISR, respectively onboard Cassini and Huygens. These data are used to check that the TheoReTS line lists are able to model observations. We also make comparisons with other experimental or theoretical line lists. It appears that TheoRetS gives very reliable results better than ExoMol and even than HITRAN2012, except around 1.6 µm where it gives very similar results. We conclude that TheoReTS is suitable to be used for the modeling of planetary radiative transfer and photometry. A re-analysis of spectra recorded by the DISR instrument during the descent of the Huygens probe suggests that the CH 4 mixing ratio decreases with altitude in Titan’s stratosphere, reaching a value of ∼ 10 − 2 above the 110 km altitude.

We report the line list for the 2v3(A1,E) and v1+v3(E) strong bands of the NF3 molecule which is considered as long living greenhouse gas in the atmosphere with a significant radiative force potential. To construct the line list, the variational calculations based on the ab initio surfaces of the potential energy and dipole moment were combined with high-resolution data on line positions. The effective polyad model was developed for NF3 by the sixth-order contact transformation of the full rovibrational Hamiltonian. The theoretical parameters of the effective Hamiltonian were then refined by fitting to experimental transitions presented in literature. The parameters of the effective dipole moment were obtained from fitting to our ab initio line intensities. The results of the simulations are consistent with our Fourier Transform spectra within their uncertainty of 10%.

Spectra of hot methane were recorded using a tube furnace and a high-resolution Fourier transform spectrometer. We obtained experimental absorption spectra in the 1.85–1.11 μm near-infrared region at eight temperatures ranging from 295 K up to 1000 K. We have converted these into an atlas of absorption cross sections at each temperature for the methane tetradecad, icosad and triacontad polyads, excluding some spectral intervals either strongly contaminated by water or due to baseline fringes. On the theoretical side, the spectra were simulated from the ab initio-based Reims-Tomsk TheoReTS line list for the same experimental conditions. This line list has been constructed by global variational calculations from potential energy and dipole moment surfaces followed by empirical line position corrections deduced from previously published analyses. The comparisons showed very good overall agreement between observations and theory at high spectral resolution for the tetradecad and icosad and at medium or low resolution above this range. A full set of the theoretical absorption cross sections is also included. Detailed temperature dependence of the methane absorption enables the efficient method of remotely probing the temperature of distant astronomical objects based on a comparison of relative signals in carefully selected spectral intervals. This first combined experimental and theoretical easy-to-use cross-section library in the near-infrared should be of major interest for the interpretation of current and future astronomical observations up to a resolving power of 100,000–300,000 in the range 6400–7600 cm−1 and a resolving power of 5000–10,000 in the higher wavenumber range up to 9000 cm−1.

In this work we report first global modeling of NF3 line positions and intensities up to the Tetradecad range of interacting bands (

Fluorine containing molecules have a particularly long atmospheric lifetime and their very big estimated global warming potentials are expected to rapidly increase in the future. This work is focused on the global theoretical prediction of infrared spectra of the tetrafluoromethane molecule that is considered as a potentially powerful greenhouse gas having the largest estimated lifetime of over 50 000 years in the atmosphere. The presence of relatively low vibrational frequencies makes the Boltzmann population of the excited levels important. Consequently, the “hot bands” corresponding to transitions among excited rovibrational states contribute significantly to the CF4 opacity in the infrared even at room temperature conditions but the existing laboratory data analyses are not sufficiently complete. In this work, we construct the first accurate and complete ab initio based line lists for CF4 in the range 0–4000 cm−1, containing rovibrational bands that are the most active in absorption. An efficient basis set compression method was applied to predict more than 700 new bands and subbands via variational nuclear motion calculations. We show that already at room temperature a quasi-continuum of overlapping weak lines appears in the CF4 infrared spectra due to the increasing density of bands and transitions. In order to converge the infrared opacity at room temperature, it was necessary to include a high rotational quantum number up to J = 80 resulting in 2 billion rovibrational transitions. In order to make the cross-section simulation faster, we have partitioned our data into two parts: (a) strong & medium line lists with lower energy levels for calculation of selective absorption features that can be used at various temperatures and (b) compressed “super-line” libraries of very weak transitions contributing to the quasi-continuum modelling. Comparisons with raw previously unassigned experimental spectra showed a very good accuracy for integrated absorbance in the entire range of the reported spectra predictions. The data obtained in this work will be made available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru) that contains ab initio born line lists and provides a user-friendly graphical interface for a fast simulation of the CF4 absorption cross-sections and radiance under various temperature conditions from 80 K to 400 K.

Accurate rovibrational analysis of the upper part of the Tetradecad 12 CH 4 spectrum in the 5855–6250 cm −1 region is reported for J ≤ 10. The analysis uses the WKLMC experimental line list previously obtained in Grenoble by Cavity Ring Down Spectroscopy and Differential laser Absorption Spectroscopy at T = 296 K. Based on a previously published ab initio potential energy surface, the full Hamiltonian of methane nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformation method with a subsequent empirical optimization of parameters. Overall, more than 3200 12 CH 4 transitions are assigned adding about 1800 new assignments to those provided in the HITRAN database for 12 CH 4 in the region. The 12 CH 4 experimental line positions were fitted with RMS standard deviations of 0.0015 cm −1 and 2381 line intensities were modeled using an effective dipole moment with the RMS deviation of 8%. Rovibrational energy levels of sixteen vibrational states of the upper part of the Tetradecad system were determined. For the first time all three sub-levels of the weak 4ν 2 band were assigned. As a result, a new version of the WKLMC list for natural methane at 296 K is provided including the new assignments in the 5855–6250 cm −1 region.

New dipole moment surfaces (DMS) of phosphine are constructed using extended ab initio CCSD(T) (CCSD(T)-F12) calculations at 11 697 nuclear configurations. The DMS analytical representation is determined through an expansion in symmetry adapted products of internal nonlinear coordinates up to the 8th order. Including high order terms permits significantly reducing the fit errors for ab initio dipole moment values in a large range of nuclear geometries. Rovibrational line strengths in the infrared are variationally computed from DMS using normal mode Eckart frame approach. Comparison of results obtained with four basis sets up to V5Z is presented. Integrated intensities of four lower PH 3 polyads up to J = 20 are in a good agreement with the HITRAN 2012 database and with available spectroscopic data analyses. A particular focus of the study is the Octad range (2650–3700 cm −1 ) containing eight interacting bands 3ν 2 , 2ν 2 + ν 4 , ν 2 + 2ν 4 , ν 1 + ν 2 , ν 2 + ν 3 , 3ν 4 , ν 3 + ν 4 and ν 1 + ν 4 , where new ab initio predictions are expected to help further analyses of experimental spectra.

In this paper, we focus on the calculations of dipole transition intensities and rovibrational spectra for 13CH4 and 12CH4. Global variational calculations of methane spectra were performed using our recent potential energy and dipole moment surfaces, combined with the tensor formalism derived in previous works. Isotopic vibrational band center shifts due to the 12C → 13C substitution were calculated up to the tetradecad range and compared with experimental values. These shifts were found to be quite irregular, but their variational predictions were very accurate, of the order ∼0.01 cm−1, and could thus be used for a precise calculation of 13CH4 line positions. Rovibrational line intensities computed from the ab initio dipole moment surfaces agree very well with those available in the HITRAN 2008 database, at least for strong and medium lines. For both isotopologues, the first comparative study of theoretical spectra with Jmax = 20 is presented up to the octad range. Our preliminary results suggest that numerous 13CH4 bands which remain still unassigned could be identified and modeled using the proposed approach.

A new study of 12CH3D line positions and intensities was performed for the upper portion of the Enneadecad polyad between 4000 and 4550/cm. For this, FTIR spectra were recorded with D-enriched methane samples (at 80 K with a Bruker 125 IFS at 0.005/cm resolution and at 291 K with the McMath-Pierce FTS at 0.011/cm resolution, respectively). Line positions and intensities were retrieved by least square curve-fitting procedures and analyzed using the effective Hamiltonian and the effective dipole moment expressed in terms of irreducible tensor operators adapted to symmetric top molecules. Initially, only the cold spectrum was used to identify quantum assignments and predict 12CH3D relative intensities in this region. To assign higher quanta up to J equal 14, additional line positions and intensities were obtained from two room temperature spectra. In the final stage, measured intensities from both the cold and the room temperature data were normalized to corresponding values at 296 K and then averaged. Combining the two temperature datasets confirmed the assumed quantum assignments and also demonstrated the relative accuracies to be better than 70.0002/cm for line positions and at least +/-6% for intensities so that approx.1160 features were selected. Including additional assignments from the room temperature spectra alone permitted 1362 line intensities of 11 bands (involving 23 vibrational symmetry components) to be reproduced with an RMS of 9%. Over 4085 selected positions for 12 bands were modeled to 0.008/cm. Nevertheless a number of known assignments could not be modeled to within our experimental precisions. More work is needed to obtain a complete characterization of this complex polyad.

International audience; We present the construction of complete and comprehensive ethylene line lists for the temperatures 50-700 K based on accurate ab initio potential and dipole moment surfaces and extensive first-principle calculations. Three lists spanning the [0-6400] cm-1 infrared region were built at T = 80, 160, and 296 K, and two lists in the range [0-5200] cm-1 were built at 500 and 700 K. For each of these five temperatures, we considered possible convergence problems to ensure reliable opacity calculations. Our final list at 700 K was computed up to J = 71 and contains almost 60 million lines for intensities I > 5 × 10-27 cm/molecule. Comparisons with experimental spectra carried out in this study showed that for the most active infrared bands, the accuracy of band centers in our theoretical lists is better on average than 0.3 cm-1, and the integrated absorbance errors in the intervals relevant for spectral analyses are about 1-3%. These lists can be applied to simulations of absorption and emission spectra, radiative and non-LTE processes, and opacity calculations for planetary and astrophysical applications. The lists are freely accessible through the TheoReTS information system at http://theorets.univ-reims.fr and http://theorets.tsu.ru

A new study of 13CH4 line intensities and positions was performed in the Octad region between 3750 and 4700 cm−1. Using 13C-enriched samples, spectra were recorded with both the McMath–Pierce FTS at Kitt Peak Observatory in Arizona and the Bruker IFS-125HR at JPL. Sample temperatures ranged between 80 and 296 K. Line positions and intensities of ~15,000 features were retrieved at different temperatures by non-linear least squares curve-fitting procedures. Intensities were used to estimate the lower state energies for 60% of the features in order to determine quantum assignments up to J=10. A preliminary analysis was performed using the effective Hamiltonian and the effective dipole transition moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. Selected assignments were made up to J=10 for all 24 sub-vibrational states of the Octad; these were modeled for 4752 experimental line positions and 3301 selected line intensities fitted with RMS standard deviations of 0.004 cm−1 and 6.9%, respectively. Integrated intensities of the eight Octad bands are compared to ab initio variational calculations. A prediction of the 13CH4 is given, but further analysis to improve the calculation will be reported in the future.

Accurate rovibrational analysis of the lower part of the Icosad 12 CH 4 spectrum in the 6539–6800 cm −1 region is reported. The analysis uses the WKLMC experimental line list previously obtained in Grenoble by Cavity Ring Down Spectroscopy and Differential Absorption Spectroscopy at T =80 K. Based on an ab initio potential energy surface, the full Hamiltonian of methane nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformations method with a subsequent empirical optimization of parameters. About 2445 experimental line positions were fitted with RMS standard deviations of 0.005 cm −1 and 1644 line intensities were modeled using effective dipole moment with the RMS deviation of 11.5%. Twenty five vibrational energy levels of the lower part of the Icosad were determined.

Two independent methods to obtain ab initio effective rotational Hamiltonians have been implemented recently. The first one is based on a generalization of perturbation theory to noncommutative rings, the other one on contact transformation (CT) techniques. In principle, both methods are able to give rotational Hamiltonians including centrifugal distortion effects of arbitrary high orders. These methods are compared, for the first time, in this article with regard to calculations of the rotational levels of methane vibrational ground state. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Variationally computed infrared spectra in the range [0-5000] cm−1 are reported for the deuterated PH2D and PHD2 molecules from accurate potential energy and dipole moment surfaces initially derived for the major isotopologue PH3(C3v). Energy level and line intensity calculations were performed by using a normal-mode model combined with isotopic and symmetry transformations for the H → D substitutions. Theoretical spectra were computed at 296 K up to Jmax = 30 and will be made available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru). For the very first time, ab initio intensity predictions of PH2D/PHD2 are in good qualitative agreement with the literature. This work will be useful for spectral intensity analysis for which accurate spectral intensity data are still missing.

A simultaneous use of the full molecular symmetry and of an exact kinetic energy operator (KEO) is of key importance for accurate predictions of vibrational levels at a high energy range from a potential energy surface (PES). An efficient method that permits a fast convergence of variational calculations would allow iterative optimization of the PES parameters using experimental data. In this work, we propose such a method applied to tetrahedral AB4 molecules for which a use of high symmetry is crucial for vibrational calculations. A symmetry-adapted contracted angular basis set for six redundant angles is introduced. Simple formulas using this basis set for explicit calculation of the angular matrix elements of KEO and PES are reported. The symmetric form (six redundant angles) of vibrational KEO without the sin(q)(-2) type singularity is derived. The efficient recursive algorithm based on the tensorial formalism is used for the calculation of vibrational matrix elements. A good basis set convergence for the calculations of vibrational levels of the CH4 molecule is demonstrated.

Accurate basis set convergence of first-principles predictions of rotationally resolved spectra at high energy range is a common challenging issue for variational methods. In this paper, a detailed convergence study for the methane spectra is presented both for vibrational and rotational degrees of freedom as well as for intensities. For this purpose, we use our previously reported nine-dimensional potential energy and dipole moment surfaces of the methane molecule [Nikitin et al. Chem Phys Lett 2011;501:179–86; 2013;565:5–11]. Vibration–rotation calculations were carried out using variational normal mode approach with a full account of the Td symmetry. The aim was to obtain accurate theoretical methane line lists for the wavenumber range beyond currently available spectra analyses. The focus of this paper is the complicated icosad range (6280–7900 cm−1) containing 20 bands and 134 sub-bands where over 90% of experimental lines still remain unassigned. We provide variational line lists converged to a “spectroscopic precision” for icosad transitions for T=80 K and T=296 K. The first one contains 70 300 lines and the second one 286 170 lines with the intensity cut-off 10 − 29 cm − 1 / ( molecule cm − 2 ) with Jmax=18. An average error in line positions of theoretical predictions up to J=15 is estimated as 0.2–0.5 cm−1 from the comparisons with currently analyzed bands. Ab initio line strength calculations give the integrated intensity 4.37 × 10 − 20 cm − 1 / ( molecule cm − 2 ) at T=80 K for the sum of all icosad bands. This is to be compared to the integrated intensity 4.36 × 10 − 20 cm − 1 / ( molecule cm − 2 ) of the experimental icosad line list recorded in Grenoble University [Campargue et al., J Mol Spectrosc 2013;291:16–22] using very sensitive laser techniques. The shapes of absorption bands are also in a good qualitative agreement with experimental spectra.

The updated methane spectral line list GOSAT-2014 for the 5550–6240 cm −1 region with the intensity cutoff of 5×10 –25 cm/molecule at 296 K is presented. The line list is based on the extensive measurements of the methane spectral line parameters performed at different temperatures and pressures of methane without and with buffer gases N 2 , O 2 and air. It contains the following spectral line parameters of about 12150 transitions: line position, line intensity, energy of lower state, air-induced and self-pressure-induced broadening and shift coefficients and temperature exponent of air-broadening coefficient. The accuracy of the line positions and intensities are considerably improved in comparison with the previous version GOSAT-2009. The improvement of the line list is done mainly due to the involving to the line position and intensity retrieval of six new spectra recorded with short path way (8.75 cm). The air-broadening and air-shift coefficients for the J -manifolds of the 2ν 3 (F 2 ) band are refitted using the new more precise values of the line positions and intensities. The line assignment is considerably extended. The lower state J -value was assigned to 6397 lines representing 94.4% of integrated intensity of the considering wavenumber region. The complete assignment was done for 2750 lines.

The near-infrared spectrum of Titan, Saturn's largest moon and one of the Cassini/Huygens' space mission primary targets, covers the 0.8 to 5 micron region in which it shows several weak CH 4 absorption regions, and in particular one centered near 2.75 micron. Due to the interference of telluric absorption, only part of this window region (2.9–3.1 μm) has previously been observed from the ground [Noll, K.S., Geballe, T.R., Knacke, R., Pendleton, F., Yvonne, J., 1996. Icarus 124, 625–631; Griffith, C.A., Owen, T., Miller, G.A., Geballe, T., 1998. Nature 395, 575–578; Griffith, C.A., Owen, T., Geballe, T.R., Rayner, J., Rannou, P., 2003. Science 300, 628–630; Geballe, T.R., Kim, S.J., Noll, K.S., Griffith, C.A., 2003. Astrophys. J. 583, L39–L42]. We report here on the first spectroscopic observations of Titan covering the whole 2.4–4.9 μm region by two instruments on board the Infrared Space Observatory (ISO) in 1997. These observations show the 2.75-μm window in its complete extent for the first time. In this study we have also used a high-resolution Titan spectrum in the 2.9–3.6 μm region taken with the Keck [Geballe, T.R., Kim, S.J., Noll, K.S., Griffith, C.A., 2003. Astrophys. J. 583, L39–L42; Kim, S.J., Geballe, T.R., Noll, K.S., Courtin, R., 2005. Icarus 173, 522–532] to infer information on the atmospheric parameters (haze extinction, single scattering albedo, methane abundance, etc.) by fitting the methane bands with a detailed microphysical model of Titan's atmosphere (updated from Rannou, P., McKay, C.P., Lorenz, R.D., 2003. Planet. Space Sci. 51, 963–976). We have included in this study an updated version of a database for the CH 4 absorption coefficients [STDS, Wenger, Ch., Champion, J.-P., 1998. J. Quant. Spectrosc. Radiat. Transfer 59, 471–480. See also http://www.u-bourgogne.fr/LPUB/TSM/sTDS.html for latest updates; Boudon, V., Champion, J.-P., Gabard, T., Loete, M., Michelot, F., Pierre, G., Rotger, M., Wenger, Ch., Rey, M., 2004. J. Mol. Spectrosc. 228, 620–634]. For the atmosphere we find that (a) the haze extinction profile that best matches the data is one with higher (by 40%) extinction in the atmosphere with respect to Rannou et al. (2003) down to about 30 km where a complete cut-off occurs; (b) the methane mixing ratio at Titan's surface cannot exceed 3% on a disk-average basis, yielding a maximum CH 4 column abundance of 2.27 km-am in Titan's atmosphere. From the derived surface albedo spectrum in the 2.7–3.08 micron region, we bring some constraints on Titan's surface composition. The albedo in the center of the methane window varies from 0.01 to 0.08. These values, compared to others reported in the other methane windows, show a strong compatibility with the water ice spectrum in the near-infrared. Without confirming its existence from this work alone, our data then appear to be compatible with water ice. A variety of other ices, such as CO 2 , NH 3 , tholin material or hydrocarbon liquid cannot be excluded from our data, but an additional unidentified component with a signature around 2.74 micron is required to satisfy the data.

The global analysis of the infrared spectrum of chloromethane involving the ground state and the 13 vibrational states lying up to 2600 cm −1 is reported. This work incorporates and extends to the fifth polyad, the preliminary study of the lower four polyads published by [J. Mol. Spectrosc. 221 (2003) 199]. More than 20 000 transitions (including numerous hot bands) for each isotopomer 12 CH 3 35 Cl and 12 CH 3 37 Cl have been assigned and fitted with a standard deviation of about 3 × 10 −4 cm −1 close to the experimental precision. A common set of 288 (resp. 303) effective parameters was determined for each isotopomer. Our global model allowed us to reproduce simultaneously and accurately the resonances already encountered in Polyad 3 and the new ones involved in Polyad 5.

A global analysis of the infrared spectrum of chloromethane involving the ground state and the 13 vibrational states lying up to 2600 cm −1 was recently achieved using high resolution Fourier transform spectra of pure isotopomers. More than 20 000 transitions (cold and hot bands) for each isotopomer 12 CH 3 35 Cl and 12 CH 3 37 Cl have been assigned and fitted with a standard deviation of about 3 × 10 −4 cm −1 close to the experimental precison. As part of this global effort, improved ground state constants up to sextic centrifugal distortion terms have been determined for each isotopomer taking advantage of the numerous allowed and perturtation-allowed transitions simultaneously fitted using our global model. The axial constants could be determined from Δ K ≠ 0 combinations arising from rovibrational local resonances within Polyads 3 and 5.

Two editions of the methane line parameters (line positions, intensities and broadening coefficients) available from HITRAN in 2000 and 2001 are described. In both versions, the spectral interval covered was the same (from 0.01 to 6184.5 cm −1 ), but the database increased from 48,033 transitions in 2000 to 211,465 lines in 2001 because weaker transitions of 12 CH 4 and new bands of 13 CH 4 and CH3D were included. The newer list became available in 2001 in the “Update” section of HITRAN. The sources of information are described, and the prospects for future improvements are discussed.

New high resolution Fourier transform spectra of pure 12CH335Cl and 12CH337Cl isotopomers of chloromethane have been recorded in Wuppertal covering the region from 600 to 3800 cm−1. New rotational transitions within the v2=1, v5=1, and v3=2 states have been measured at Lille. A first global analysis of the lower four band systems of the molecule (700–1800 cm−1) is reported. The model was based on an effective Hamiltonian and dipole moment expressed in terms of irreducible tensor operators. A common set of 125 effective hamiltonian parameters (sixth order) has been adjusted to fit simultaneously some 11 000 IR data for each of the isotopomers including 153 mm wave data for 12 CH3 35 Cl. The assignments involve 12 sets of transitions (6 cold bands, 3 hot bands, and 3 pure rotational systems for 12CH335Cl). The standard deviation was on average 0.00014 cm−1 and 175 kHz for the IR and MMW data, respectively. The v3=v6=1 state was analysed for the first time principally from observed hot band transitions.

As part of the simultaneous analysis of line positions and intensities of the first two polyads of monodeuterated methane, the results achieved for the 3 to 5 mu m region are reported.

A new study of 12CH4 line positions and intensities was performed for the lower portion of the Tetradecad region between 4800 and 5300 cm−1 using long path (1603 m) spectra of normal sample CH4 at three pressures recorded with the Fourier transform spectrometer in Reims, France. Line positions and intensities were retrieved by least square curve-fitting procedures and analyzed using the effective Hamiltonian and the effective Dipole moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. An existing spectrum of enriched 13CH4 was used to discern the isotopic lines. A new measured linelist produced positions and intensities for 5851 features (a factor of two more than prior work). Assignments were made for 46% of these; 2725 experimental line positions and 1764 selected line intensities were fitted with RMS standard deviations of 0.004 cm−1 and 7.3%, respectively. The RMS of prior intensity fits of the lower Tetradecad was previously a factor of two worse. The sum of observed intensities between 4800 and 5300 cm−1 fell within 5% of the predicted value from variational calculations.

The high resolution absorption spectrum of CH(sub 3)D in the region of 900-1700 cm(sup -1) has been revisited on the basis of new long path experimental data recorded with the Fourier transform spectrometer at Kitt Peak. A theoretical model used previously for spherical rotors has been adapted for polyatomic molecules in order to analyze the vibrational polyads of CH(sub 3)D simultaneously.

Improved algorithms for the construction of rovibrational operators of polyatomic molecules are presented. Vibrationally diagonal and off-diagonal terms are obtained by a specific coupling scheme of creation and annihilation elementary operators. Recursive procedures are used to generate all possible terms and associated basis functions as well as to calculate matrix elements and commutators. Explicit formulations are given forTd,Oh, andC3vmolecules.

0019-1035/$ see front matter 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.icarus.2013.07.015 DOI of original article: http://dx.doi.org/10.1016/j.icarus.2013.05.033 ⇑ Corresponding author. Address: LESIA, Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France. Fax: +33 145072806. E-mail address: bruno.bezard@obspm.fr (B. Bezard). 1 Present address: Foundation ‘‘La main a la pâte’’, Montrouge, France. M. Hirtzig , B. Bezard a,⇑, E. Lellouch , A. Coustenis , C. de Bergh , P. Drossart , A. Campargue , V. Boudon , V. Tyuterev , P. Rannou , T. Cours , S. Kassi , A. Nikitin , D. Mondelain , S. Rodriguez , S. Le Mouelic g

International audience; During the last 4 years, empirical line lists for methane at room temperature and at 80 K were constructed from spectra recorded by (i) differential absorption spectroscopy (DAS) in the high energy part of the tetradecad (5852-6195 cm-1) and in the icosad (6717-7589 cm-1) and (ii) high sensitivity CW-Cavity Ring Down Spectroscopy (CRDS) in the 1.58 μm and 1.28 μm transparency windows (6165-6750 cm-1 and 7541-7919 cm-1, respectively). We have recently constructed the global line lists for methane in "natural" isotopic abundance, covering the spectral region from 5854 to 7919 cm-1 (Campargue A, Wang L, Kassi S, Mondelain D, Bézard B, Lellouch E, et al., An empirical line list for methane in the 1.26-1.71 μm region for planetary investigations (T=80-300 K). 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±3 K and 296±3 K, 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 6500 cm-1.The new version of our lists at 80 K and 296 K 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 80 K list the 27,580 single lines present only in the 296 K list, with corresponding lower state energy values chosen to make them below the detectivity limit at 80 K.In the discussion, the different line lists and databases available for methane in the near infrared are compared and some suggestions are given.

International audience; In this paper we apply a recently released set of methane line parameters (Wang et al., 2011) to the modeling of Titan spectra in the 1.58 mu m window at both low and high spectral resolution. We first compare the methane absorption based on this new set of methane data to that calculated from the methane absorption coefficients derived in situ from DISR/Huygens (Tomasko et al., 2008a; Karkoschka and Tomasko, 2010) and from the band models of Irwin et al. (2006) and Karkoschka and Tomasko (2010). The Irwin et al. (2006) band model clearly underestimates the absorption in the window at temperature-pressure conditions representative of Titan's troposphere, while the Karkoschka and Tomasko (2010) band model gives an acceptable agreement in the whole window, overestimating the absorption by about 15% in the range 6300-6500 cm(-1). We also find that the transmittance of Titan's atmosphere is in excellent agreement with that calculated from the Tomasko et al. (2008a) coefficients after reducing them by about 7%. Synthetic spectra computed with spectral resolutions of 1.2 cm(-1) (R similar to 5400) and 0.35 cm(-1) (R similar to 18000) are then compared with two high-resolution Earth-based measurements of Titan's albedo obtained in 1982 and 1993 (with KPNO/FTS and IRTF/CSHELL). The new set of methane line parameters leads to an excellent match of all the CH3D and CH4 absorption features in these spectra, and permits us to derive a ratio of CH3D/CH4=(4.5 +/- 1.0) x 10(-4) - hence a D/H ratio in methane for Titan of (1.13 +/- 0.25) x 10(-4) - and a CO mole fraction of 40 +/- 10 ppm (from the KPNO/FTS dataset) and 51 +/- 7 ppm (from the IRTF/CSHELL dataset). We also infer constraints on the far-wing lineshape of methane lines of the 2v(3) band. We finally present two other examples of models of Titan's spectrum using the new line parameters, one potentially useful for future higher-resolution (R=40,000) observations, another one applicable to the ongoing low-resolution (R similar to 100) observations by Cassini VIMS. We show that the aerosol model of Tomasko et al. (2008b) produces too much intensity at low phase angle compared to a VIMS spectrum recorded near the Huygens site and we propose a slightly revised model that reproduces this observation.

The MIRS software for the modeling of ro-vibrational spectra of polyatomic molecules was considerably extended and improved. The original version (Nikitin, et al. JQSRT, 2003, pp. 239--249) was especially designed for separate or simultaneous treatments of complex band systems of polyatomic molecules. It was set up in the frame of effective polyad models by using algorithms based on advanced group theory algebra to take full account of symmetry properties. It has been successfully used for predictions and data fitting (positions and intensities) of numerous spectra of symmetric and spherical top molecules within the vibration extrapolation scheme. The new version offers more advanced possibilities for spectra calculations and modeling by getting rid of several previous limitations particularly for the size of polyads and the number of tensors involved. It allows dealing with overlapping polyads and includes more efficient and faster algorithms for the calculation of coefficients related to molecular symmetry properties (6C, 9C and 12C symbols for C_{3v}, T_{d}, and O_{h} point groups) and for better convergence of least-square-fit iterations as well. The new version is not limited to polyad effective models. It also allows direct predictions using full ab initio ro-vibrational normal mode hamiltonians converted into the irreducible tensor form. Illustrative examples on CH_{3} D, CH_{4}, CH_{3} Cl, CH_{3} F and PH_{3} are reported reflecting the present status of data available. It is written in C++ for standard PC computer operating under Windows. The full package including on-line documentation and recent data are freely available at [http://www.iao.ru/mirs/mirs.htm] or [http://xeon.univ-reims.fr/Mirs/||http://xeon.univ-reims.fr/Mirs/] or [http://icb.u-bourgogne.fr/OMR/SMA/SHTDS/MIRS.html]., Journal of Quantitative Spectroscopy and Radiative Transfer (2012) xxx-xxx

T.D.S. is a computer package concerned with high resolution spectroscopy of spherical top molecules like CH 4 , CF 4 , SiH 4 , SiF 4 , SnH 4 , GeH 4 , SF 6 , etc. T.D.S. contains information, fundamental spectroscopic data (energies, transition moments, spectroscopic constants) recovered from comprehensive modeling and simultaneous fitting of experimental spectra, and associated software written in C. The T.D.S. goal is to provide an access to all available information on vibration-rotation molecular states and transitions including various spectroscopic processes (Stark, Raman, etc.) under extended conditions based on extrapolations of laboratory measurements using validated theoretical models. Applications for T.D.S. may include: education/training in molecular physics, quantum chemistry, laser physics; spectroscopic applications (analysis, laser spectroscopy, atmospheric optics, optical standards, spectroscopic atlases); applications to environment studies and atmospheric physics (remote sensing); data supply for specific databases; and to photochemistry (laser excitation, multiphoton processes). The reported DOS-version is designed for IBM and compatible personal computers.

International audience; This paper reports the first assignment of rovibrational transitions of the 54 and 2+44 band systems of 12CH4 in the 6287-6550 cm-1 region which is usually referred to as part of the 1.6 m methane transparency window. The analysis was based on two line lists previously obtained in Grenoble by Cavity Ring Down Spectroscopy at T= 297 K and 79 K completed by three long path Fourier Transform Spectra recorded in Reims (L=1603 m, P= 1-34 mbar). In order to determine the dipole transition moment parameters and quantify the intensity borrowing due to the resonance interactions, we had to include in the fit of the effective Hamiltonian model some lines of the stronger 1+34 and 2+44 bands. For this purpose, intensities of 179 additional lines were retrieved from FTS spectra above 6550 cm-1 though the analysis of these higher bands is not complete. About 1955 experimental line positions and 1462 line intensities were fitted with RMS standard deviations of 0.003 cm-1 and 13.4%, respectively. A line list of 8027 calculated and observed transitions which are considered as dominant was constructed for 12CH4 in the 6287-6550 cm-1 region. This is the first high-resolution analysis and modeling of 5-quanta band systems of 12CH4.

International audience; A theoretical approach to study ro-vibrational molecular states from a full nuclear Hamiltonian expressed in terms of normal-mode irreducible tensor operators is presented for the first time. Each term of the Hamiltonian expansion can thus be cast in the tensor form in a systematic way using the formalism of ladder operators. Pyramidal XY3 molecules appear to be good candidates to validate this approach which allows taking advantage of the symmetry properties when doubly degenerate vibrational modes are considered. Examples of applications will be given for PH3 where variational calculations have been carried out from our recent potential energy surface [Nikitin et al., J. Chem. Phys. 130, 244312 (2009)].

International audience; In order to model the high-resolution infrared spectrum of the phosphine molecule in the 3 mu m region, a global approach involving the lower three polyads of the molecule (Dyad, Pentad and Octad) as been applied using an effective hamiltonian in the form of irreducible tensors. This model allowed to describe all the 15 vibrational states involved and to consider explicitly all relevant ro-vibrational interactions that cannot be accounted for by conventional perturbation approaches. 2245 levels (up to J=14) observed through transitions arising from 34 cold and hot bands including all available existing data as well as new experimental data have been fitted simultaneously using a unique set of effective hamiltonian parameters. The rms achieved is 0.63 10^{-3} cm^{-1} for 450 Dyad levels, 1.5 10^{-3} cm^{-1} for 1058 Pentad levels (from 3585 transitions) and 4.3 10^{-3} cm^{-1} for 737 Octad levels (from 2243 transitions). This work represents the first theoretical modeling of the 3 mu m region. It also improves the modeling of the region around 4.5 mu m by dividing the rms reported by previous works by a factor 6. A preliminary intensity analysis based on consistent sets of effective dipole moment operators for cold and hot bands has been simultaneously undertaken for direct comparison between observed and modeled absorption from 700 to 3500 cm^{-1}.

International audience; The infrared spectrum of CH3D from 3250 to 3700 cm(-1) was studied for the first time to assign transitions involving the nu(2) + nu(3), nu(2) + nu(5), nu(2) + nu(6), nu(3) + 2(nu 6) and 3 nu(6) vibrational states. Line positions and intensities were measured at 0.011 cm(-1) resolution using Fourier transform spectra recorded at Kitt Peak with isotopically enriched samples. Some 2852 line positions (involving over 900 upper state levels) and 874 line intensities were reproduced with RMS values of 0.0009 cm(-1) and 4.6%, respectively. The strongest bands were found to be nu(2) + nu(3) at 3499.7 cm(-1) and nu(2) + nu(6) at 3342.5 cm(-1) with integrated strengths, respectively, of 8.17 x 10(-20) and 2.44 x 10(-20) (cm(-1)/ molecule center . cm(-2)) at 296 K (for 100% CH3D). The effective Hamiltonian was expressed in terms of irreducible tensor operators and adapted to symmetric top molecules. Its present configuration in the MIRS package permitted simultaneous consideration of the four lowest polyads of CH3D: the Ground State (G.S.), the Triad from 6.3 to 9.5 mu m, the Nonad from 3.1 to 4.8 mu m and now the Enneadecad (19 bands) from 2.2 to 3.1 mu m. The CH3D line parameters for this interval were calculated to create a new database for the 3 mu m region.

International audience; The current version GEISA-97 of the computer-accessible database system GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information) is described. This catalogue contains 1,346,266 entries. These are spectroscopic parameters required to describe adequately the individual spectral lines belonging to 42 molecules (96 isotopic species) and located between 0 and 22,656 cm-1. The featured molecules are of interest in studies of the terrestrial as well as the other planetary atmospheres, especially those of the Giant Planets. GEISA-97 contains also a catalog of absorption cross-sections of molecules such as chlorofluorocarbons which exhibit unresolvable spectra. The modifications and improvements made to the earlier edition (GEISA-92) and the data management software are described. GEISA-97 and the associated management software are accessible from the ARA/LMD (Laboratoire de Météorologie Dynamique du CNRS, France) web site: http://ara01.polytechnique.fr/registration.

A nearly Doppler-limited spectrum of the 2ν 3 band of the 12 CF 4 molecule between 2536.0 and 2599.8 cm −1 was recorded at T = 77 K using difference-frequency laser spectroscopy. The simultaneous analysis of the ground (G.S.), ν 3 = 1, and ν 3 = 2 states was performed using an isolated band model to sixth order in the tetrahedral formalism. Fourteen hundred seventy-five transitions were assigned through J = 35 to the F 2 and E vibrational components of the ν 3 = 2 level. A total of 1864 transition frequencies were fit simultaneously (1000 2ν 3 - G.S. newly assigned transitions together with 575 ν 3 - G.S. and 289 ν 3 - ν 3 transitions already reported in the literature). The ground state constants were improved. Interactions with the ν 3 + 2ν 4 and 4ν 4 bands are proposed to explain some of the discrepancies observed in the 2ν 3 band.

A rovibrational model based on the normal-mode complete nuclear Hamiltonian is applied to methane using our recent potential energy surface [A. V. Nikitin, M. Rey, and Vl. G. Tyuterev, Chem. Phys. Lett. 501, 179 (2011)]. The kinetic energy operator and the potential energy function are expanded in power series to which a new truncation-reduction technique is applied. The vibration-rotation Hamiltonian is transformed systematically to a full symmetrized form using irreducible tensor operators. Each term of the Hamiltonian expansion can be thus cast in the tensor form whatever the order of the development. This allows to take full advantage of the symmetry properties for doubly and triply degenerate vibrations and vibration-rotation states. We apply this model to variational computations of energy levels for (12)CH(4), (13)CH(4), and (12)CD(4).