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International audience; Measurements in the rotationally-resolved Q branch of the Raman spectrum of the fundamental vibration ( v = 0 -> v = 1 ) of N 2 perturbed by CO have been conducted at three temperatures, 77, 195 and 298 K, in order to obtain broadening and mixing coefficients for the different rovibrational lines observed. In parallel with these measurements, calculations have also been performed on the system at the same three temperatures to obtain theoretical values for the coefficients. The experiments have been carried out using high-resolution stimulated Raman spectroscopy (SRS), while for the calculations two different approaches have been explored: a quantum dynamical calculation and a parametric one utilizing the energy-corrected sudden (ECS) approximation. Comparison between experiment and calculations show good agreement for both the quantum dynamical and the ECS calculated values. This is, to our knowledge, the first reported experimental determination of collisional line broadening and mixing coefficients in the spectrum of N 2 perturbed by CO. We also present a brief comparison with the results of prior calculations and with measurements conducted not long ago in the reverse collisional system (i.e., CO perturbed by N 2 ).

International audience; We present a theoretical evaluation of collision induced effects on a few typical doublets in the nu_4 band of ammonia perturbed by argon.Quantum dynamical calculations performed on two NH_3-Ar potential energy surfaces provide pressure broadening and intradoublet generalized cross sections. From these calculations we derive thermally averaged values at various temperatures. The intradoublet coupling terms at room temperature are found to be in good agreement with available data in the literature. In addition, we study the speed dependence of the pressure broadening and intradoublet coupling coefficients. The former show a usual speed dependence, quite important, but the later show a weak speed dependence at least around 296 K and above.

The CO2 molecule is of great interest for astrophysical studies since it can be found in a large variety of astrophysical media where it interacts with the dominant neutral species, such as He, H2, or H2O. The CO2–He collisional system was intensively studied over the last two decades. However, collisional data appear to be very sensitive to the potential energy surface (PES) quality. Thus, we provide, in this study, a new PES of the CO2–He van der Waals complex calculated with the coupled-cluster method and a complete basis set extrapolation in order to provide rotational rate coefficients that are as accurate as possible. The PES accuracy was tested through the calculations of bound state transition frequencies and pressure broadening coefficients that were compared to experimental data. An excellent agreement was globally found. Then, revised collisional data were provided for the 10–300 K temperature range. Rate coefficients were compared to previously computed ones and are found to be up to 50% greater than previously provided ones. These differences can induce non-negligible consequences for the modeling of CO2 abundance in astrophysical media.

International audience; We investigate collisional line-shape effects that are present in highly accurate experimental spectra of the 3-0 S(1) and 2-0 Q(1) molecular hydrogen absorption lines perturbed by helium. We clearly distin-guish the influence of six different collisional effects (i.e.: collisional broadening and shift, their speed dependencies and the complex Dicke effect) on the shapes of H-2 lines. We demonstrate that only a very specific combination of these six contributions, determined from our ab initio calculations, gives unprece-dentedly good agreement with experimental spectra. If any of the six contributions is neglected, then the experiment-theory comparison deteriorates at least several times. We also analyze the influence of the centrifugal distortion on our ab initio calculations and we demonstrate that the inclusion of this effect slightly improves the agreement with the experimental spectra. (C) 2021 The Author(s). Published by Elsevier Ltd.

A proper description of the collisional perturbation of the shapes of molecular resonances is important for remote spectroscopic studies of the terrestrial atmosphere. Of particular relevance are the collisions between the O

International audience; A proper description of the collisional perturbation of the shapes of molecular resonances is important for remote spectroscopic studies of the terrestrial atmosphere. Of particular relevance are the collisions between the O2 and N2 molecules—the two most abundant atmospheric species. In this work, we report a new highly accurate potential energy surface and use it for performing the first quantum scattering calculations addressing line shapes for this system. We use it to model the shape of the 118 GHz fine structure line in O2 perturbed by collisions with N2 molecules, a benchmark system for testing our methodology in the case of an active molecule in a spin triplet state. The calculated collisional broadening of the line agrees well with the available experimental data over a wide temperature range relevant for the terrestrial atmosphere. This work constitutes a step toward populating the spectroscopic databases with ab initio line shape parameters for atmospherically relevant systems. © 2021 Author(s).

International audience; HCN and its unstable isomer HNC are widely observed throughout the interstellar medium, with the HNC/HCN abundance ratio correlating strongly with temperature. In very cold environments HNC can even appear more abundant than HCN. Here we use a chirped pulse Fourier transform spectrometer to measure the pressure broadening of HCN and HNC, simultaneously formed in situ by laser photolysis and cooled to low temperatures in uniform supersonic flows of helium. Despite the apparent similarity of these systems, we find the HNC-He cross section to be more than twice as big as the HCN-He cross section at 10 K, confirming earlier quantum calculations. Our experimental results are supported by high-level scattering calculations and are also expected to apply with para-H-2, demonstrating that HCN and HNC have different collisional excitation properties that strongly influence the derived interstellar abundances.

H2 is a benchmark system for fundamental physics, yet spectroscopy is hindered by the lack of dipole moment. We present a comb-calibrated coherent Raman spectrometer for advanced studies of the collisional physics of the molecule.

We report fully quantum calculations of the collisional perturbation of a molecular line for a system that is relevant for Earth's atmosphere. We consider the N

15 pags., 12 figs., 6 tabs., We present a joint experimental and theoretical study of line broadening and mixing in the Q branch of the Raman spectrum of CO perturbed by N at 77, 195 and 298 K. Advanced methods and facilities have been used for both aspects of the study: the experiments were conducted using a high-resolution stimulated Raman spectroscopy setup, while the calculations were performed using a quantum dynamical formalism and one of the most recent potential energy surfaces available. Line broadening coefficients were determined experimentally for rovibrational lines up to j=11 at 77 K, j=15 at 195 K and j=19 at 298 K, and calculated for lines up to j=6 at the three temperatures. Line mixing was also observed and coefficients measured for lines up to j=8 at 77 K and j=5 at 195 K, and again calculated up to j=6 at the three temperatures. A comparison shows an overall very good agreement between experiments and calculations for both sets of coefficients. Additional calculated data for the pure rotational R and S lines are also provided., D. Paredes-Roibás and R. Z. Martínez acknowledge the fund- ing received from Project FIS2017-84391-C2-1-P of Ministerio de Economía y Competitividad. H. Józwiak’s contribution is supporte by the National Science Centre in Poland through Project No. 2018/31/B/ST2/00720.

International audience; We report a comprehensive dataset of beyond-Voigt line-shape parameters (pressure broadening and shift coefficients, their speed-dependences, and the complex Dicke parameters) for all electric dipole and quadrupole transitions within the ground electronic state in He-perturbed HD that are present in the HITRAN database. The parameters are determined from generalized spectroscopic cross-sections which we obtain by solving ab initio quantum scattering problem using the close-coupling formulation and the state-of-the-art potential energy surface of the HD-He interaction. We parametrize the temperature dependence of the line-shape parameters with double-power-law representation (DPL), recommended for the HITRAN database. Comparison with the analogous results for the H-2-He system reveals a strong isotopologue dependence. (C) 2021 The Authors. Published by Elsevier Ltd.

International audience; We use three independent spectroscopic techniques, operating in the millimeter-wavelength range, to study molecule-atom collisions, and validate our quantum-scattering calculations on two recent potential energy surfaces. We study the first pure rotational transition in a CO molecule perturbed by Ar. This molecular system is a good prototype of atmospherically relevant cases. It is, on the one hand, affordable for calculation of the line shape parameters by modern ab initio methods, and on the other hand, is very convenient for experimental studies because of its regular, well spaced rotational spectrum having a moderate intensity. We show that the simulated collision-perturbed spectra, which are based on our fully ab initio calculations, agree with the experimental line profiles at sub-percent level over a wide range (more than four orders of magnitude) of pressures. We demonstrate that the agreement between theory and experiment can be further improved if the model accounts for the collisional transfer of an optical coherence between different rotational transitions (the line-mixing effect). We show that the two surfaces tested in this work lead to a very similar agreement with the experiment. Capability of calculating line shape parameters in a broad range of temperatures is demonstrated.

International audience; We present fully ab initio calculations of second-overtone rovibrational line shapes of carbon monoxide perturbed by argon. The quantum mechanical scattering problem between CO and Ar is solved numerically for two different ab initio interaction potentials. We use the generalized Hess method to determine spectroscopic cross sections which describe the effect of collisions on each spectral line. Using these cross sections, we determine the line-shape parameters that we use to generate the Hartmann-Tran and speed-dependent billiard ball profiles. We compare the generated line shapes with high-quality experimental line profiles of five lines measured at five pressures between 0.01 and 1 atm. A subpercent agreement over the entire pressure range is obtained. Calculations for the P(9) line are used to inspect the effects of the two interaction potentials. The discrepancies for both the considered interaction potentials and the experiment are explained within the described theoretical framework. The presented results are the most accurate collisional line-shape calculations for a system with collision dynamics representative of atmospherically relevant species.

International audience; We report ab initio calculations of generalized spectroscopic cross-sections for hydrogen deuteride perturbed by helium. From these calculations, collisional line-shape parameters are deduced for the HD electric dipole transitions from R(0) to R(5) and from P(1) to P(6) in the 0–0 to 5–0 bands. These parameters are necessary for a proper interpretation of HD spectra from the atmospheres of gas giants. We demonstrate that the centrifugal distortion cannot be ignored, not only for pure rotational lines but also for rovibrational lines when one aims at sub–percent accuracy of the collisional line–shape parameters.

We present accurate measurements of the quadrupole S(3) and S(4) transitions of the ${\mathrm{D}}_{2}\phantom{\rule{4pt}{0ex}}2\ensuremath{-}0$ band. Self-perturbed spectra were collected in a wide pressure range with a cavity ring-down spectrometer linked to an optical frequency comb. The results of ab initio quantum scattering calculations were incorporated into the line-shape analysis which was performed using the Hartmann-Tran profile. This approach allowed us to mitigate the collisional systematics and to reach a 900-kHz accuracy of the transition frequencies, which represents a 30-fold improvement compared to previously available data. We also compare our findings with newly calculated transition frequencies that include relativistic and quantum electrodynamics corrections up to ${\ensuremath{\alpha}}^{7}$. The differences between theoretical and experimental values for the transition frequencies are 2.2 MHz and 3.3 MHz for the S(3) and S(4) transitions, respectively.

International audience; Fully quantum ab initio calculations of the collision-induced shapes of two rovibrational H-2 lines perturbed by He provide an unprecedented subpercent agreement with ultra-accurate cavity-enhanced measurements. This level of consistency between theory and experiment hinges on a highly accurate potential energy surface and a realistic treatment of the velocity changing and dephasing collisions. In addition to the fundamental importance, these results show that ab initio calculations can provide reference data for spectroscopic studies of planet atmospheres at the required accuracy level and can be used to populate spectroscopic line-by-line databases.

International audience; Temperature dependences of molecular line-shape parameters are important for the spectroscopic studies of the atmospheres of the Earth and other planets. A number of analytical functions have been proposed as candidates that may approximate the actual temperature dependences of the line-shape parameters. In this article, we use our ab initio collisional line-shape calculations for several molecular systems to compare the four temperature ranges (4TR) representation, adopted in the HITRAN database [J. Quant. Spectrosc. Radiat. Transfer 2017;203:3] in 2016, with the double-power-law (DPL) representation. Besides the collisional broadening and shift parameters, we consider also the most important line-shape parameters beyond Voigt, i.e., the speed dependence of broadening and shift parameters, and real and imaginary parts of the complex Dicke parameter. We demonstrate that DPL gives better overall approximation of the temperature dependencies than 4TR. It should be emphasized that DPL requires fewer parameters and its structure is much simpler and more self-consistent than the structure of 4TR. We recommend the usage of DPL representation in HITRAN, and present DPL parametrization for Voigt and beyond-Voigt line profiles that will be adopted in the HITRAN database. We also discuss the problem of the Hartmann-Tran profile parametrization in which the correlation parameter, η, and frequency of the velocity-changing collisions parameter, ν vc , diverges to infinity when collisional shift crosses zero; we recommend a simple solution for this problem.

International audience; We review progress, since publication of the book "Collisional effects on molecular spectra Laboratory experiments and models, consequences for applications" (Elsevier, Amsterdam, 2008), on measuring, modeling and predicting the influence of pressure (ie of intermolecular collisions) on the spectra of gas molecules. We first introduce recently developed experimental techniques of high accuracy and sensitivity. We then complement the aforementioned book by presenting the theoretical approaches, results and data proposed (mostly) in the last decade on the topics of isolated line shapes, line-broadening and-shifting, line-mixing, the far wings and associated continua, and collision-induced absorption. Examples of recently demonstrated consequences of the progress in the description of spectral shapes for some practical applications (metrology, probing of gas media, climate predictions) are then given. Remaining issues and directions for future research are finally discussed.

International audience; This work presents a comparison between experimental and calculated values for the collisional line broadenings and shifts of the S-0(0), S-0(1), and S-0(2) lines of the rotational Raman spectrum of D-2 perturbed by He at 77, 195, and 300K. The pure rotational Raman spectra were obtained by means of a stimulated Raman spectroscopy experimental setup. Close coupling dynamical calculations were performed on the most recent ab initio H-2-He potential energy surface. The resulting scattering matrix elements implemented in the general Hess method allow us to provide pressure broadening, pressure shifting, and Dicke coefficients from 10 to 400K. Experimental and calculated values agree well with each other.

International audience; We present a procedure for generating the parameters of the Hartmann-Tran profile (HTP) from purely first principles calculations. Starting from an absorber-perturber interaction potential, we calculate S-matrices describing the effect of collisions on the absorbing molecule. We then use the generalized Hess method to calculate speed-dependent pressure shift and broadening parameters, and the complex Dicke parameter, ν opt , which accounts for such effects as the Dicke effect and correlations between dephasing and velocity-changing collisions. Based on these ab initio results, we derive the Hartmann-Tran profile parameters and evaluate the validity of the quadratic approximation of speed dependence and the hard-collision model of velocity-changing collisions adopted in the Hartmann-Tran profile. We also discuss the interpretation and speed dependence of ν opt. Finally, we evaluate the approximation scheme for temperature dependence of HTP line-shape parameters adopted in the 2016 edition of the HITRAN database.

Synopsis We demonstrate the results of the first ab initio investigation of the line-shape parameters for two molecular systems important for atmospheric studies: CO-N2 and O2-N2. We provide the pressure broadening and shift coefficients with their speed dependencies for purely rotational lines, calculated from highly accurate potential energy surfaces with the close-coupling scheme. This is the first, fully quantum approach to the problem of determination of the spectral line shapes for the systems important for terrestrial atmospheric measurements.

Synopsis We present the methodology of obtaining the dataset of the beyond-Voigt line-shape parameters for spectroscopic databases from fully ab initio quantum-scattering calculations. It provides not only the pressure broadening and shift coefficients, but also their speed dependencies and the complex Dicke parameter. This approach is based on the calculations of the generalized spectroscopic cross section, resulting from the close-coupling equations solved for a given scattering system. The calculations were validated on accurate experimental spectra of the helium-perturbed hydrogen molecule.

H 2 is the simplest neutral molecule in the universe and it is a benchmark system for testing quantum electrodynamics and physics beyond the standard model via highly accurate measurements of its transition frequencies [1–3], However, the retrieval of unperturbed transition frequencies is hampered by the weakness of quadrupole transition moments, which determines poor signal-to-noise ratios at low pressure. Alternatively, it is possible to precisely model the H 2 lineshapes at higher pressure in order to account for the strong collisional effects that distort the absorption profile and eventually extrapolate by proper fitting an accurate line centre.

International audience

International audience; We report fully quantum calculations of the collisional perturbation of a molecular line for a system that is relevant for Earth's atmosphere. We consider the N2-perturbed pure rotational R(0) line in CO. The results agree well with the available experimental data. This work constitutes a significant step toward populating the spectroscopic databases with ab initio collisional line-shape parameters for atmosphere-relevant systems. The calculations were performed using three different recently reported potential energy surfaces (PESs). We conclude that all three PESs lead to practically the same values of the pressure broadening coefficients. © 2021 Author(s).

We demonstrate a new method for populating line-by-line spectroscopic databases with beyond-Voigt line-shape parameters, which is based on ab initio quantum scattering calculations. We report a comprehensive dataset for the benchmark system of He-perturbed H2 (we cover all the rovibrational bands that are present in the HITRAN spectroscopic database). We generate the entire dataset of the line-shape parameters (broadening and shift, their speed dependence, and the complex Dicke parameter) from fully ab initio quantum-scattering calculations. We extend the previous calculations by taking into account the centrifugal distortion for all the bands and by including the hot bands. The results are projected on a simple structure of the quadratic speed-dependent hard-collision profile. We report a simple and compact formula that allows the speed-dependence parameters to be calculated directly from the generalized spectroscopic cross sections. For each line and each line-shape parameter, we provide a full temperature dependence within the double-power-law (DPL) representation, which makes the dataset compatible with the HITRAN database. The temperature dependences cover the range from 20 to 1000 K, which includes the low temperatures relevant for the studies of the atmospheres of giant planets. The final outcome from our dataset is validated on highly accurate experimental spectra collected with cavity ring-down spectrometers. The methodology can be applied to many other molecular species important for atmospheric and planetary studies.

12 pags., 15 figs., 3 tabs., 2 apps., We report theoretical and experimental line-shape parameters for He-perturbed pure rotational HD lines that are relevant for the studies of gas giants atmospheres. Besides the usual pressure broadening and shift parameters, we also report their speed dependencies and Dicke parameters. The theoretical values, obtained from quantum dynamical calculations, are for the R(j=0-3) lines and S(j=0-2) and temperatures from 10 to 500 K. The measurements, performed using stimulated Raman spectroscopy, were done for the S(j=0-2) rotational Raman lines at 77, 195 and 298 K. We also compare the results of our calculations with pressure broadening and line shift coefficients available in the literature at 77, 195 and 300 K for the studied R lines. We demonstrate that a simple Voigt profile is insufficient to accurately model the shapes of He-perturbed HD lines at conditions relevant to gas giants atmospheres, and one should incorporate also the speed-dependent effects and velocity-changing collisions., RZM and DB acknowledge the funding received from Project FIS2017-84391-C2-1-P of Ministerio de Economía y Competitividad.PW contributionis supported by the National Science Centre in Poland through Projects Nos. 2015/19/D/ST2/02195 and 2018/31/B/ST2/00720. The project is cofinanced by the Polish National Agency forAcademic Exchange under the PHC Polonium program (dec. PPN/X/PS/318/2018). PW and FT are supported by the French-Polish PHC Polonium program (project42769ZKfortheFrenchpart)

International audience; We have analyzed 10 room temperature spectra of the fundamental band of CO and CO-air using the Voigt, speed-dependent Voigt, speed-dependent Rautian line shape models. Line positions, intensities, air- and self-broadening coefficients, pressure induced air- and self-shift coefficients, and line-mixing parameters have been retrieved. The CO- and N2-broadened carbon monoxide half width coefficients have been calculated using a potential energy surface based on Tipping-Herman intermolecular interaction potential and taking the electrostatic interactions into account. © Published under licence by IOP Publishing Ltd.

3 pags., 1 fig., 2 tabs.-- International Conference on Spectral Lines Shapes 17–22 June 2018, Dublin City University, Ireland, We review our recent experimental and theoretical studies on the spectral line shapes of D2 in helium baths. We also provide the most accurate to date experimental line positions of the first pure rotational Stokes lines, S0(j=0-2), of D2., RZM and DBP acknowledge the funding received from Vicepresidencia de Investigación Cientifica y Técnica of Consejo Superior de Investigaciones Científicas through the Fondo de Apoyo Extraordinario and from Project FIS2017-84391-C2-1-P of Ministerio de Economía y Competitividad. PW contribution is supported by the National Science Centre, Poland, Project no. 2015/19/D/ST2/02195.

We review our recent studies on the spectral line shapes of H2, including its isotopologues, self-perturbed or perturbed by helium. Line shape parameters are derived following the generalized Hess method and making use of the close-coupling formalism.

International audience

3 pags., 1 tab., We present accurate measurements for the wavenumbers of the S(0), S(1), and S(2) pure rotational Raman lines in D. Our measurements improve the accuracy of the previously available experimental data by an order of magnitude. They also show complete agreement with the state-of-the-art ab initio calculations of the D rotational splitting, which include both relativistic and Quantum electrodynamics (QED) corrections., R. Z. M. and D. B. P. acknowledge the funding received from Vicepresidencia de Investigación Cientifica y Técnica of Consejo Superior de Investigaciones Científicas through the Fondo de Apoyo Extraordinario and from Project FIS2017-84391-C2-1-P of Ministerio de Economía y Competitividad. P. W. contribution is supported by the National Science Centre, Poland, Project No. 2015/19/D/ST2/02195.

International audience; Lorentz self- and H2-broadened half-width and pressure-induced shift coefficients, line mixing coefficients as well as line center positions and intensities were obtained using a nonlinear least square fitting technique for 48 (P(24) to R(23)) ro-vibrational transitions belonging to the first overtone (2←0) band of 12C16O at room temperature. All spectra in the 4146 to 4332 cm−1 spectral interval were fitted simultaneously employing four line shape functions: the Voigt, Speed Dependent Voigt, Rautian and Speed Dependent Rautian profiles. The collisional line mixing effect has been observed and investigated as an asymmetry in the analyzed line profiles. A semi-empirical Exponential Power Gap Law method was used to estimate the self- and H2-broadening coefficients and the collisional line mixing parameters. Additionally, a classical approach was applied to calculate the half-width coefficients of transitions in the 2←0 band for carbon monoxide broadened by H2 and for pure CO. The classical approach based on a simple computational method, ensures the molecular motion is correctly characterized in 3 dimensions. The calculations used vibrationally independent intermolecular interaction potentials. The variation of CO half-width coefficients with rotational quantum number J ≤ 24 was computed and compared with measurements. The agreement between the theoretical broadening coefficients is better for pure CO rather than for the CO-H2 system.

International audience; We present our experimental spectra of the very weak S(2) transition from the 2–0 band of molecular deuterium, measured with a frequency-stabilized cavity ring-down spectroscopy (FS–CRDS) assisted by the optical frequency comb (OFC). Experimental collisional broadening and shifting are compared with results of ab initio quantum scattering calculations.

The close-coupling method is used to calculate purely rotational relaxation rates and pressure broadening and shifting coefficients for H2-He collisions, in order to test various potential energy surfaces. Downward rate coefficients k 3→1(T) and k 2→0(T) are compared with experimental data, but the subtle differences in the potential energy surfaces are hardly reflected in these rates. Helium pressure broadening and shifting generalized cross sections for the isotropic Raman Q(1) lines of the fundamental bands of D2 and H2 as well as the purely rotational Stokes S0(1) line of H2 are therefore also considered. While these spectroscopic characteristics are much more sensitive to the precise form of the interaction potential, a proper validation cannot be performed without taking into account the influence of the translational motion on the molecular line shapes. After including this, it is found that the potential energy surface of Bakr, Smith and Patkowski [B.W. Bakr, D.G.A. Smith, K. Patkowski, J. Chem. Phys. 139, 144305 (2013)] allows the best reproduction of the experimental data.