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arXiv · 1802.07566

Electron-impact excitation of diatomic hydride cations II: OH$^+$ and SH$^+$

James R Hamilton·Alexandre Faure·Jonathan Tennyson
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Abstract

R-matrix calculations combined with the adiabatic-nuclei-rotation and Coulomb-Born approximations are used to compute electron-impact rotational rate coefficients for two open-shell diatomic cations of astrophysical interest: the hydoxyl and sulphanyl ions, OH$^+$ and SH$^+$. Hyperfine resolved rate coefficients are deduced using the infinite-order-sudden approximation. The propensity rule $ΔF=Δj=ΔN=\pm 1$ is observed, as is expected for cations with a large dipole moment. A model for OH$^+$ excitation in the Orion Bar photon-dominated region (PDR) is presented which nicely reproduces Herschel observations for an electron fraction $x_e=10^{-4}$ and an OH$^+$ column density of $3\times 10^{13}$~cm$^{-2}$. Electron impact electronic excitation cross sections and rate coefficients for the ions are also presented.

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James R Hamilton, Alexandre Faure, Jonathan Tennyson. 2018-02-21. Electron-impact excitation of diatomic hydride cations II: OH$^+$ and SH$^+$. https://doi.org/10.1093/mnras%2Fsty437

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