Electron-impact excitation of diatomic hydride cations - I. HeH⁺, CH⁺, ArH⁺

James R. Hamilton , Alexandre Faure (1) , Jonathan Tennyson

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

R-matrix calculations combined with the adiabatic nuclei approximation are used to compute electron-impact rotational excitation rates for three closed-shell diatomic cations, HeH⁺, CH⁺, ArH⁺. Comparisons with previous studies show that an improved treatment of threshold effects leads to significant changes in the low temperature rates; furthermore the new calculations suggest that excitation of CH⁺ is dominated by ΔJ = 1 transitions as is expected for cations with a large dipole moment. A model for ArH⁺ excitation in the Crab nebula is presented which gives results consistent with the observations for electron densities in the range 2-3 × 10³ cm^-3.

Keywords: molecular processes; ISM: molecules; Astrophysics - Astrophysics of Galaxies

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

James R. Hamilton, Alexandre Faure, Jonathan Tennyson. Electron-impact excitation of diatomic hydride cations - I. HeH⁺, CH⁺, ArH⁺. Monthly Notices of the Royal Astronomical Society, 2016, 455, pp.3281-3287. ⟨10.1093/mnras/stv2429⟩. ⟨insu-03691576⟩