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Molecular collisions are manifested as a perturbation of the shapes of molecular optical resonances. Therefore, on the one hand, the line-shape analysis of accurate molecular spectra constitutes an important tool for studying quantum scattering and testing ab initio molecular interactions [1]. On the other hand, the collisional effects can deteriorate the accuracy of atmospheric measurements of the Earth and other planets, modify the opacity of the exoplanetary atmospheres as well as influence the accuracy in optical metrology based on molecular spectroscopy [2,3]. Recently a new relational structure has been introduced to the most extensively-used line-by-line spectroscopic database HITRAN [4,5], enabling the collisional, beyond-Voigt line-shape effects to be represented. It is, however, extremely challenging to populate the entire database with purely experimental parameters for all the molecular transitions and thermodynamical conditions (all the bands, branches and temperature ranges).
We demonstrate a new methodology of generating a comprehensive dataset of the beyond-Voigt line-shape parameters from fully ab initio quantum-scattering calculations. We also demonstrate first such a complete dataset for the benchmark system of helium-perturbed H2 line. We provide the temperature dependences for the pressure broadening and shift parameters, as well as for the Dicke parameter using generalized spectroscopic cross sections resulting from quantum scattering calculations on accurate ab initio potential energy surfaces. The results are consistent with the recently adapted HITRAN parameterisation of the Hartmann-Tran profile [4]. The calculations and methodology are also validated on the ultra-accurate experimental data of the H2-He system.
References
[1] Wcisło P et al. 2015 Phys. Rev. A 91, 052505.
[2] Moretti L et al. 2013 Phys. Rev. Lett. 111, 060803.
[3] Wcisło P et al. 2016 Phys. Rev. A 93, 022501.
[4] Wcisło P et al. 2016 J. Quant Spectrosc. Radiat. Transfer 177, 75-91.
[5] Gordon I E et al. 2017 J. Quant. Spectrosc. Radiat. Transfer 203, 3 – 69. 3
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