The effect of water and electron collisions in the rotational excitation of HF in comets

J. Loreau (1) , A Faure (2) , François Lique (3)

1 KU Leuven - Catholic University of Leuven - Katholieke Universiteit Leuven
2 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
3 IPR - Institut de Physique de Rennes

We present the first set of rate coefficients for the rotational excitation of the 7 lowest levels of hydrogen fluoride (HF) induced by collision with water molecules, the dominant collider in cometary comas, in the 5-150 K temperature range. The calculations are performed with a quantum statistical approach from an accurate rigid rotor ab initio interaction potential. Rate coefficients for excitation of HF by electron-impact are also computed, within the Born approximation, in the 10-10 000 K temperature range. These rate coefficients are then used in a simple non-local thermodynamic equilibrium (non-LTE) model of a cometary coma that also includes solar radiative pumping and radiative decay. We investigate the range of H₂O densities that lead to non-LTE populations of the rotational levels of HF. We show that to describe the excitation of HF in comets, considering collisions with both water molecules and electrons is needed as a result of the large dipole of HF.

Keywords: molecular data; molecular processes; scattering; comets: general; Astrophysics - Earth and Planetary Astrophysics; Physics - Chemical Physics; Quantum dynamics

Domains: Sciences of the Universe [physics]; Physics [physics]

J. Loreau, A Faure, François Lique. The effect of water and electron collisions in the rotational excitation of HF in comets. Monthly Notices of the Royal Astronomical Society, 2022, 516, pp.5964-5971. ⟨10.1093/mnras/stac2378⟩. ⟨insu-03860258⟩