Hyperfine excitation of SH⁺ by H

¹ LOMC – UMR 6294, CNRS-Université du Havre, 25 rue Philippe Lebon, BP 1123, 76 063 Le Havre cedex, France
e-mail: francois.lique@univ-lehavre.fr
² Instituto de Física Fundamental, CSIC, C/Serrano, 123, 28006 Madrid, Spain
³ Departamento de Quimica Fisica, Facultad de Ciencias Quimicas, Universidad de Salamanca, 37008 Salamanca, Spain
⁴ Firat University, Department of Physics, 23169 Elazi, Turkey

Received: 27 March 2020
Accepted: 24 April 2020

Abstract

Context. SH⁺ is a surprisingly widespread molecular ion in diffuse interstellar clouds. There, it plays an important role by triggering the sulfur chemistry. In addition, SH⁺ emission lines have been detected at the UV-illuminated edges of dense molecular clouds, so-called photo-dissociation regions (PDRs), and toward high-mass protostars. An accurate determination of the SH⁺ abundance and of the physical conditions prevailing in these energetic environments relies on knowing the rate coefficients of inelastic collisions between SH⁺ molecules and hydrogen atoms, hydrogen molecules, and electrons.

Aims. We derive SH⁺–H fine and hyperfine-resolved rate coefficients from recent quantum calculations for the SH⁺–H collisions, including inelastic, exchange, and reactive processes.

Methods. The method we used is based on the infinite-order sudden approach.

Results. State-to-state rate coefficients between the first 31 fine levels and 61 hyperfine levels of SH⁺ were obtained for temperatures ranging from 10 to 1000 K. Fine-structure resolved rate coefficients present a strong propensity rule in favor of Δj = ΔN transitions. The Δj = ΔF propensity rule is observed for the hyperfine transitions.

Conclusions. The new rate coefficients will help significantly in the interpretation of SH⁺ spectra from PDRs and UV-irradiated shocks where the abundance of hydrogen atoms with respect to hydrogen molecules can be significant.