Issue 8, 2018

Fine-structure transitions of interstellar atomic sulfur and silicon induced by collisions with helium

Abstract

Atomic sulfur and silicon are important constituents of the interstellar matter and are both used as tracers of the physical conditions in interstellar shocks and outflows. We present an investigation of the spin–orbit (de-)excitation of S(3P) and Si(3P) atoms induced by collisions with helium with the aim to improve the determination of atomic sulfur and silicon abundances in the interstellar medium from S and Si emission spectra. Quantum-mechanical calculations have been performed in order to determine rate coefficients for the fine-structure transitions in the 5–1000 K temperature range. The scattering calculations are based on new highly correlated ab initio potentials. The theoretical results show that the (de-)excitation of Si is much faster than that of S. The rate coefficients deduced from this study are in good agreement with previous experimental and theoretical findings despite some deviations at low temperatures. From the computation of critical densities defined as the ratios between Einstein coefficients and the sum of the relevant collisional de-excitation rate coefficients, we show that local thermodynamic equilibrium conditions are not fulfilled for analyzing S and Si emission spectra observed in the interstellar medium. Hence, the present rate coefficients will be extremely useful for the accurate determination of interstellar atomic sulfur and silicon abundances.

Graphical abstract: Fine-structure transitions of interstellar atomic sulfur and silicon induced by collisions with helium

Supplementary files

Article information

Article type
Paper
Submitted
27 srp 2017
Accepted
26 ruj 2017
First published
26 ruj 2017

Phys. Chem. Chem. Phys., 2018,20, 5427-5434

Fine-structure transitions of interstellar atomic sulfur and silicon induced by collisions with helium

F. Lique, J. Kłos and S. D. Le Picard, Phys. Chem. Chem. Phys., 2018, 20, 5427 DOI: 10.1039/C7CP05092E

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements