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We present ab initio calculations of the collisional broadening of the R(0) pure rotational line in CO (at 115 GHz) perturbed by O

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).

Calculations of hyperfine splittings in ${\mathrm{H}}_{2}$ are needed for an accurate experimental determination of frequencies of rovibrational transitions and the dissociation energy in ${\mathrm{H}}_{2}$, which are used for experimental tests of quantum electrodynamics for molecules and for searches for new physics beyond the standard model. While the hyperfine structure of the ground electronic $X^{1}\mathrm{\ensuremath{\Sigma}}_{g}^{+}$ state in ${\mathrm{H}}_{2}$ has been studied in detail, there are no theoretical or experimental data regarding the excited electronic $^{1}\mathrm{\ensuremath{\Sigma}}_{g}^{+}$ states. Here, we report the first investigation of the hyperfine structure of rovibrational levels in the excited double-well $EF^{1}\mathrm{\ensuremath{\Sigma}}_{g}^{+}$ state in the hydrogen molecule. We provide hyperfine splittings and coupling constants for several low-lying rovibrational levels. The hyperfine splittings in the inner well are approximately 1 order of magnitude larger than those in the outer well and 2 times smaller than those in the ground electronic state.

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.

We perform a theoretical investigation of hyperfine structure of all rovibrational quadrupole transitions in the ground electronic 1 Σ + state of the HD molecule. We determine positions and intensities of 185 631 hyperfine components of 7 251 quadrupole rovibrational transitions from the O, Q and S branches. Moreover, we provide a list of hyperfine splittings of all bound states in the six isotopologues of hydrogen which we considered in previous papers. The results reported here are necessary for a reliable interpretation of accurate experimental studies of rovibrational transition frequencies in the HD isotopologue, which are useful for tests of quantum electrodynamics for molecules and searches for new physics beyond the Standard Model.

We report a list of positions and intensities of 331 892 hyperfine components of all 18 585 rovibrational dipole transitions in the HT and DT isotopologues of molecular hydrogen. Apart from the study of hyperfine structure, we investigate the intensities of all rovibrational dipole transitions in the two isotopologues, which were not known prior to this work. The results presented here are crucial for a reliable interpretation of accurate measurements of rovibrational transition frequencies in the tritium-bearing isotopologues of hydrogen, which are useful for tests of quantum electrodynamics for molecules and searches for new physics beyond the Standard Model.

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.

We report results of a theoretical investigation of hyperfine interactions in two homonuclear isotopologues of the hydrogen molecule: H$_{2}$ and D$_{2}$. We present a set of hyperfine coupling constants: spin-rotation, spin-spin dipole and, in the case of the D$_{2}$ molecule, electric quadrupole coupling constants for all bound states of the two isotopologues in their ground electronic $X^{1}\Sigma^{+}_{g}$ state. We provide a list of positions and intensities of 220 997 hyperfine components of 16 079 rovibrational quadrupole transitions of the O, Q and S branches. The positions and intensities of the hyperfine components are necessary for a reliable interpretation of accurate measurements of rovibrational transition frequencies in H$_{2}$ and D$_{2}$, which are used for tests of the quantum electrodynamics of molecules and searches for new physics beyond the Standard Model.

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.

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.

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.

We perform a theoretical investigation of hyperfine interactions in the tritium-bearing isotopologues of the hydrogen molecule: HT, DT and T2. We report a set of hyperfine coupling constants: spin-rotation, spin-spin dipole and, in the case of the DT isotopologue, electric quadrupole coupling constants for all bound states of the three isotopologues in their ground electronic states. We determine positions and intensities of 656 217 hyperfine components of 38 971 quadrupole rovibrational transitions from the O, Q and S branches. The positions and intensities of the hyperfine components are necessary for a reliable interpretation of accurate measurements of rovibrational transition frequencies in tritium-bearing isotopologues of hydrogen, which are useful for tests of quantum electrodynamics for molecules and searches for new physics beyond the Standard Model.

We report results of a theoretical analysis of hyperfine interactions in the HD molecule. We present the calculated coupling constants: spin-rotation, spin-spin and electric quadrupole coupling constants for all bound states of HD in its ground electronic 1Σ state. We provide a list of positions and intensities of 108 320 hyperfine components of 5 129 dipole transitions from the P and R branches. The positions and intensities of the hyperfine components are necessary for a proper interpretation of accurate measurements of rovibrational transition frequencies in HD which are used for tests of quantum electrodynamics of molecules and searches for new physics beyond the Standard Model.