Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007a%26a...472.1037v&link_type=abstract
Astronomy and Astrophysics, Volume 472, Issue 3, September IV 2007, pp.1037-1040
Astronomy and Astrophysics
Astrophysics
8
Ism: Molecules, Molecular Data, Molecular Processes
Scientific paper
Context: Observations of molecular emission at millimeter and infrared wavelengths, supplemented by careful and detailed modeling, are powerful tools for investigating the physical and chemical conditions of astrophysical objects. Modeling of molecular emission requires excitation calculations using radiative as well as collisional rates with the most abundant species. Aims: The present paper focuses on the calculation of rate coefficients among the first rotational levels of the SiS molecule in its ground vibrational state in collision with He. Methods: A new accurate two dimensional potential energy surface system was calculated for the SiS-He system using highly correlated ab initio calculations. Dynamical calculations of pure rotational (de)excitation of SiS by collisions with He were performed for the first rotational levels using the near exact close-coupling approach. Results: Collisional cross sections among the 26 first rotational levels of SiS were calculated for kinetic energies up to 1500 cm-1. Rate coefficients between the rotational levels were calculated for temperatures ranging from 5 to 200 K. A propensity rule that favors even Δ j transitions is found and is explained by the small asymmetry of the SiS-He potential energy surface.
Lique François
Spielfiedel A.
Vincent F. M. L.
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