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The paper describes methods and fast computational algorithm for building effective Hamiltonians in molecular physics using perturbative approach. Separations of fast and slow variables are considered in the framework of contact transformations (CT). The particular focus is on a systematic derivation of effective models for rovibrational spectroscopy from ab initio-based potential energy surfaces with an exhaustive review of previous studies in this field. We consider applications to several types of polyads coupled by Fermi, Coriolis, Darling-Dennison and other types of resonance interactions with examples for asymmetric top, symmetric top and spherical top molecules. A flexible choice of the modelling operator accounts for strong couplings of various types of nuclear motion in molecules among closely lying levels including vibrational resonance schemes (2:1:2 . . . ), (2:1:2:1), (4:2:6:3), (3:2:1:2:1:1), etc. that occur for C-2v, C-3v and T-d molecules and their isotopic species. The method is implemented in the MOL_CT programme suite, which offers a complementary tool to variational methods in terms of convergence and computational time. The range of applications is also different. The goal of the CT method is providing mathematical models for analyses of molecular spectra with the high-resolution accuracy using physically meaningful parameters derived from ab initio functions.

This paper describes the 2020 release of the GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), developed and maintained at LMD since 1974. GEISA is the reference database for several current or planned Thermal and Short-Wave InfraRed (TIR and SWIR) space missions IASI (Infrared Atmospheric Sounding Interferometer), IASI-NG (IASI New Generation), MicroCarb (Carbon Dioxide Monitoring Mission), Merlin (MEthane Remote sensing LIdar missioN). It is actually a compilation of three databases: the “line parameters database”, the “cross-section sub-database” and the “microphysical and optical properties of atmospheric aerosols sub-database”. The new edition concerns only the line parameters dataset, with significant updates and additions implemented using the best available spectroscopic data. The GEISA-2020 line parameters database involves 58 molecules (145 isotopic species) and contains 6,746,987 entries, in the spectral range from 10−6 to 35877 cm−1. In this version, 23 molecules have been updated (with 10 new isotopic species) and 6 new molecules have been added (HONO, COFCl, CH3F, CH3I, RuO4, H2C3H2 (isomer of C3H4)) corresponding to 15 isotopic species. The compilation can be accessed through the AERIS data and services center for the atmosphere website (https://geisa.aeris-data.fr/), with the development of a powerful graphical tool and convenient searching, filtering, and plotting of data using modern technologies (PostgreSQL database, REST API, VueJS, Plotly). Based on four examples (H2O, O3, O2 and SF6), this paper also shows how the LMD in house validation algorithm SPARTE (Spectroscopic Parameters And Radiative Transfer Evaluation) helps to evaluate, correct, reject or defer the input of new spectroscopic data into GEISA and this, thanks to iterations with researchers from different communities (spectroscopy, radiative transfer).

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.

The pump-probe technique for investigating vibrationally excited states via high resolution Raman spectroscopy was applied to CH methane isotopologue. The dipole transitions between A totally symmetric vibrational states are not active in IR spectra but these states can be efficiently studied using selective high resolution Raman spectroscopy. 80 vibration-rotation transitions, most of which belong to the 2ν– ν band have been assigned in the observed Raman spectra reported in this work. Including the Raman transitions in the simultaneous data fit improves the accuracy of the effective Hamiltonian and also rovibrational upper state levels of the ν, 2ν and 2ν (A) bands. A more accurate model of the ν vibration-rotation transitions improves the interpretation of the temperature dependence of Raman spectra involving the Pentad and Tetradecad polyads., Part of the research was performed at Institute of Monitoring of Climatic and Ecological Systems under contract of Russian Science Foundation (RSF), grant No. 19-77-10046. The research at the V.E. Zuev Institute of Atmospheric Optics was supported by the Ministry of Science and Higher Education of the Russian Federation (V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Sciences). The supports of the CNRS (France) in the frame of “Laboratoire International Associé SAMIA”, of IDRIS / CINES computer centers of France and of the ROMEO computer center Reims-Champagne-Ardenne are acknowledged. R.Z. Martínez, D. Paredes-Roibás and D. Bermejo acknowledge the funding received from Project FIS2017-84391-C2-1-P of Ministerio de Economía y Competitividad.

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.

Internal vibrational and rotational partition functions are calculated for nine molecules that are abundant in the terrestrial atmosphere and some are also observed in planetary and exoplanet atmospheres. These molecules are often observed in non-local thermodynamic equilibrium (NLTE) conditions. Calculations are made for all isotopologues of these molecules for which data are available, generally for the temperature range T = 1–5000 K. The methods of calculation of the vibrational and rotational partition functions, Qv and Qr, respectively, the convergence, and the uncertainties for each isotopologue are discussed. Finally, a FORTRAN program, NLTE_TIPS_2021.FOR, to recall the NLTE partition sums is discussed.

A 15-dimensional analytical form for the potential energy and dipole moment surfaces of the SF6 molecule in the ground electronic state is obtained using ab initio methods. In order to calculate th...

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.

International audience; In this work, we present a global view of the impact of isotopic substitutions on eleven ethylene isotopologues spectra obtained from variational calculations using accurate ab initio potential energy and dipole moment surfaces. That may lead to some important changes in molecular spectra due to symmetry breaking eects lowering the initial D 2h symmetry of 12 C 2 H 4 (≡ 12 CH 2 12 CH 2) to C 2v ,C 2h or C s. For the very rst time, we report ab initio predictions for 12 C 2 D 4 (≡ 12 CD 2 12 CD 2) and three C s species : 12 CHD 13 CH 2 , 13 CHD 12 CH 2 and 12 C 2 HD 3 (≡ 12 CD 2 12 CHD). To this end, we have considered the normal-mode approach based on our reduced Eckart-Watson Hamiltonian combined with ethylene ab initio surfaces. This work will contribute to the complete theoretical studies of the deuterated and 13 C-enriched ethylene isotopologues. A total of 1252 vibrational levels is computed and all the corresponding transitions in the energy range ≤ 3100 cm −1 are predicted and compared to 151 bands assigned from experimental spectra analyses.

This paper is devoted to the application of methods for contours and shapes comparison of objects represented as two-dimensional point clouds obtained during segmentation of data from a laser scanning system. The methods considered allow estimating the displacement of objects in the field of view of the scanning system. Methods are considered on the basis of Euclidean distances, Hausdorff metrics, invariant moments and shape context.

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.

In this work, we propose an algorithm for calculating the matrix elements of the kinetic energy operator for tetrahedral molecules. This algorithm uses the dependent six-angle coordinates (6A) and takes into account the full symmetry of molecules. Unlike A.V. Nikitin, M. Rey, and Vl. G. Tyuterev who operate with the kinetic energy operator only in Radau orthogonal coordinates, we consider a general case. The matrix elements are shown to be a sum of products of one-dimensional integrals.

Due to the importance of methane as a trace atmospheric gas and a greenhouse gas, we have carried out a precise line-shape study to obtain the CH 4 –CH 4 and CH 4 –air half-width coefficients, CH 4 –CH 4 and CH 4 –air shift coefficients and off-diagonal relaxation matrix element coefficients for methane transitions in the spectral range known as the “ methane Octad ”. In addition, the associated temperature dependences of these coefficients have been measured in the 4300–4500 cm −1 region of the Octad. The high signal to noise ratio spectra of pure methane and of dilute mixtures of methane in dry air with high resolution have been recorded at temperatures from 148 K to room temperature using the Bruker IFS 125 HR Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory, Pasadena, California. The analysis of spectra was done using a multispectrum non-linear least-squares curve fitting technique. Theoretical calculations have been performed and the results are compared with the previously published line positions, intensities and with the line parameters available in the GEISA and HITRAN2012 databases.

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.

Parameters of line positions and line intensities up to 2×10 –25 cm −1 /(molecule cm −2 ) for 12 CH 3 35 Cl and 12 CH 3 37 Cl were retrieved from the Fourier transform spectra in the range of 1900–2600 cm −1 . Line intensities were scaled with measurements from literature. Measured line positions and intensities were treated using global effective Hamiltonian and dipole moment model. The RMS of intensity fitting was 7.4% for 12 CH 3 35 Cl and 6.6% for 12 CH 3 37 Cl. List of positions and intensities were calculated for 22,098 and 21,014 lines between 1900 and 2600 cm −1 for 12 CH 3 35 Cl and 12 CH 33 7 Cl, respectively. Updated intensities allow extending assignments. The new line list of positions and intensities for both isotopologues in this spectral region was calculated. The calculations from the line list of this work have been compared with values from the HITRAN2012 database and PNNL spectra.

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

Nine-dimensional potential energy surface (PES) and dipole moment surface (DMS) of the germane molecule are constructed using extended ab initio CCSD(T) calculations at 19 882 points. PES analytical representation is determined as an expansion in nonlinear symmetry adapted products of orthogonal and internal coordinates involving 340 parameters up to eighth order. Minor empirical refinement of the equilibrium geometry and of four quadratic parameters of the PES computed at the CCSD(T)/aug-cc-pVQZ-DK level of the theory yielded the accuracy below 1 cm–1 for all experimentally known vibrational band centers of five stable isotopologues of 70GeH4, 72GeH4, 73GeH4, 74GeH4, and 76GeH4 up to 8300 cm–1. The optimized equilibrium bond re = 1.517 594 Å is very close to best ab initio values. Rotational energies up to J = 15 are calculated using potential expansion in normal coordinate tensors with maximum errors of 0.004 and 0.0006 cm–1 for 74GeH4 and 76GeH4. The DMS analytical representation is determined through an expansion in symmetry-adapted products of internal nonlinear coordinates involving 967 parameters up to the sixth order. Vibration–rotation line intensities of five stable germane isotopologues were calculated from purely ab initio DMS using nuclear motion variational calculations with a full account of the tetrahedral symmetry of the molecules. For the first time a good overall agreement of main absorption features with experimental rotationally resolved Pacific Northwest National Laboratory spectra was achieved in the entire range of 700–5300 cm–1. It was found that very accurate description of state-dependent isotopic shifts is mandatory to correctly describe complex patterns of observed spectra at natural isotopic abundance resulting from the superposition of five stable isotopologues. The data obtained in this work will be made available through the TheoReTS information system.

The GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information) has been developed and maintained by the ARA/ABC(t) group at LMD since 1974. GEISA is constantly evolving, taking into account the best available spectroscopic data. This paper presents the 2015 release of GEISA (GEISA-2015), which updates the last edition of 2011 and celebrates the 40th anniversary of the database. Significant updates and additions have been implemented in the three following independent databases of GEISA. The “line parameters database” contains 52 molecular species (118 isotopologues) and transitions in the spectral range from 10−6 to 35,877.031 cm−1, representing 5,067,351 entries, against 3,794,297 in GEISA-2011. Among the previously existing molecules, 20 molecular species have been updated. A new molecule (SO3) has been added. HDO, isotopologue of H2O, is now identified as an independent molecular species. Seven new isotopologues have been added to the GEISA-2015 database. The “cross section sub-database” has been enriched by the addition of 43 new molecular species in its infrared part, 4 molecules (ethane, propane, acetone, acetonitrile) are also updated; they represent 3% of the update. A new section is added, in the near-infrared spectral region, involving 7 molecular species: CH3CN, CH3I, CH3O2, H2CO, HO2, HONO, NH3. The “microphysical and optical properties of atmospheric aerosols sub-database” has been updated for the first time since 2003. It contains more than 40 species originating from NCAR and 20 from the ARIA archive of Oxford University. As for the previous versions, this new release of GEISA and associated management software facilities are implemented and freely accessible on the AERIS/ESPRI atmospheric chemistry data center website., SCOPUS: ar.j, info:eu-repo/semantics/published

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.

A detailed study of methane spectra in the highly congested icosad range of 6280-7800 cm(-1) has been performed using global variational calculations derived from accurate ab initio potential energy and dipole moment surfaces. About 13,000 (12)CH4 lines of the WKLMC line lists recorded at 80 and 296 K using very sensitive laser techniques (DAS, CRDS) have been rovibrationally assigned from first principles predictions. Overall, a total of 7436 upper energy levels were determined. Among the 20 bands and the 134 sub-levels contained in the icosad system, 20 and 108 have been identified for the first time, respectively. The assigned transitions represent 98% of the sum of the experimental intensity at 80 K. This work demonstrates for the first time how accurate first principles global calculations allow assigning complicated spectra of a molecule with more than 4 atoms.

The 13CH4 absorption spectrum has been recorded at 296 K and 80 K in the Icosad range between 6600 and 7700 cm−1. The achieved noise equivalent absorption of the spectra recorded by differential absorption spectroscopy (DAS) is about αmin ≈ 1.5 × 10−7 cm−1. Two empirical line lists were constructed including 17,792 and 24,139 lines at 80 K and 296 K, respectively. For comparison, the HITRAN database provides only 1040 13CH4 lines in the region determined from methane spectra with natural isotopic abundance. Empirical values of the lower state energy level, Eemp, were systematically derived from the intensity ratios of the lines measured at 80 K and 296 K. Overall 10,792 Eemp values were determined providing accurate temperature dependence for most of the 13CH4 absorption in the region (93% and 82% at 80 K and 296 K, respectively). The quality of the derived empirical values of the lower state rotational quantum number, Jemp, is illustrated by their clear propensity to be close to an integer. A good agreement is achieved between our small Jemp values, with previous accurate determinations obtained by applying the 2T method to jet and 80 K spectra. The line lists at 296 K and 80 K which are provided as Supplementary material will be used for future rovibrational assignments based on accurate variational calculations.

The absorption spectrum of water vapor enriched by deuterium and oxygen-18 is analyzed in the 6000–9200 cm−1 region. The spectrum has been recorded at room temperature with a Bruker IFS 120 h Fourier transform spectrometer. More than 14,000 absorption lines were measured in the recorded spectrum. The vibration–rotation assignments were performed on the basis of previously published experimental energies and of variational calculations. Nine water species (H216O, HD16O, D216O, H218O, HD18O, D218O, H217O, HD17O and D217O) were found to contribute to the observed absorption. More than 3600 lines of 19 vibrational bands of D218O and about 4700 lines of 16 bands of HD18O with J as high as 19 and Ka as high as 11 were assigned. The main part of the HD18O and D218O lines and all lines of HD17O and D217O were observed in the laboratory for the first time. The obtained vibration–rotation energy levels are compared with previous experimental studies and the results of variational calculations.

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

A new potential energy surface of methane is constructed using extended ab initio CCSD(T) calculations at 19 882 points. Its analytical representation is determined through an expansion in symmetry adapted products of orthogonal coordinates involving 276 parameters up to 8th order with the equilibrium bond re = 1.08601 ± 0.00004 A and four quadratic parameters scaled to experimental fundamental vibration frequencies. Variational calculations give RMS (obs.-calc.) deviations of 0.085 and 0.25 cm−1 for vibration levels of the pentad and octad. Rotational energies up to J = 10 are calculated using potential expansion in normal coordinate tensors with maximum errors of 0.0007 and 0.0003 cm−1 for 12CH4 and 13CH4.

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 methane spectral line list for the 5550–6236 cm −1 range with the intensity cut off 4×10 −26 cm/molecule at 296 K is presented. The line list is based on new extensive measurements of methane spectral line parameters performed at different temperatures and pressures of methane and buffer gases N 2 , O 2 and air. This spectral line list is prepared in HITRAN-2008 format and contains the following spectral line parameters of about 11,000 lines: position, intensity, energy for lower state (where possible), air-broadening and air-shifting coefficients, exponent of temperature dependence of air-broadening coefficient and self-broadening coefficient.

The absorption spectra of the 12CH4 and 13CH4 molecules have been recorded and assigned in the 5560–6200 cm−1 region. The effects of isotopic substitution for 12C by 13C on the methane vibrational energy levels have been calculated from an ab initio potential energy surface and compared with experiment. Comparison of the results obtained for two isotopic species allows us to confirm the vibrational assignment for the strongest bands of 12CH4 in this region. Good agreement of ab initio calculations with observed energy levels has been demonstrated. A list of the assigned 13CH4 lines valuable in atmospheric applications is reported.

The absorption spectra of mixtures of methane (CH 4 ) with N 2 and O 2 at different partial pressures of both CH 4 and buffer gases for three temperatures 240, 267, and 296 K have been recorded using the Bruker IFS 125 HR FTIR spectrometer in the 5550–6236 cm −1 region. The multispectrum fitting procedure has been applied to these spectra to recover the spectral line parameters. The main goal of this procedure was the determination of the N 2 - and O 2 -broadening and shifting coefficients and the exponents of their temperature dependences. These parameters have been derived for 452 assigned lines with good values of the signal to noise ratio. The rotational dependence of the mean values of these parameters is discussed. The temperature dependence exponents were observed for both N 2 and O 2 buffer gases.

The vibrational levels for two isotopic species of methyl chloride have been calculated in the region 0–3500 cm −1 from the ab initio potential energy surface (PES). The isotopic shift of vibrational levels of molecules 12 CH 3 35 Cl and 12 CH 3 37 Cl has been calculated. The correlation consistent basis sets cc-pVTZ and cc-pVQZ are employed to calculate energy values for 7957 and 3758 points correspondingly from a large domain of the nine-dimensional internal coordinate space. The analytic global PES is fitted with the standard deviation of 4.5 cm −1 .

International audience; Accurate ab initio full-dimensional dipole moment surfaces of ethylene are computed at 82 542 nuclear configurations using coupled-cluster approach and its explicitly correlated counterpart CCSD(T)-F12 combined respectively with ccpVQZ and cc-pVTZ-F12 basis sets. Their analytical representations are provided through 4-th order normal mode expansions. First-principles predictions of line intensities in rotationally resolved spectra using variational method up to J = 30 are in excellent agreement with experimental data in the range 0-3200 cm−1. Errors of 0.25 - 6.75% in integrated intensities for fundamental bands are comparable with experimental uncertainties. Overall calculated C2H4 opacity in 600-3300 cm−1 range agrees with experimental determination better than to 0.5%. The improved accuracy permitted to resolve some controversial issues related to the qualitative behavior of intensity patterns.

We report the variationally computed infrared spectrum of (12)CH2D2 using our recent potential energy and dipole moment methane surfaces, which have been initially derived in the irreducible tensor representation adapted to the tetrahedral symmetry of the major isotopologue (12)CH4. The nuclear motion calculations are accomplished by combining the normal-mode Eckart-Watson Hamiltonian with isotopic and symmetry transformations. Our direct vibrational calculations are compared to the 93 observed band centers up to 6300 cm(-1). Except for two outliers the root-mean-square deviation is 0.22 cm(-1) and the maximum error is 0.7 cm(-1) without empirical adjustment of parameters. The work aims at filling the gap concerning missing line strength information for this molecule. Theoretical spectra predictions are given up to J = 25 and, for the very first time, ab initio intensity predictions for rovibrational line transitions are in good qualitative agreement with available experimental spectra.

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.