Hyperfine excitation of SH${}^{+}$ by H

Abstract

SH${}^{+}$ is a surprisingly widespread molecular ion in diffuse interstellar clouds. There, it plays an important role triggering the sulfur chemistry. In addition, SH${}^{+}$ emission lines have been detected at the UV-illuminated edges of dense molecular clouds, \mbox{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. In this paper, we derive SH${}^{+}$--H fine and hyperfine-resolved rate coefficients from the recent quantum calculations for the SH${}^{+}$--H collisions, including inelastic, exchange and reactive processes. The method used is based on the infinite order sudden approach. 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 favour of $\Delta j=\Delta N$ transitions. The $\Delta j=\Delta F$ propensity rule is observed for the hyperfine transitions. {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.

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Cited by in corpus (2)

• Bottlenecks to interstellar sulfur chemistry: Sulfur-bearing hydrides in UV-illuminated gas and grains
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