Journal Article

Rotationally and torsionally inelastic scattering of methanol on helium

Djamal Rabli and D. R. Flower

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 411, issue 3, pages 2093-2098
Published in print March 2011 | ISSN: 0035-8711
Published online February 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17842.x
Rotationally and torsionally inelastic scattering of methanol on helium

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Cross-sections and rate coefficients have been computed for rotationally and torsionally inelastic transitions between levels of the torsional manifolds ν= 0, 1 and 2 of methanol; the collision partner was the helium atom. We find the torsional inelasticity to be most pronounced for transitions between the excited states, ν= 1 and 2. The torsionally inelastic cross-sections are smaller, on average, than the cross-sections for pure rotationally inelastic transitions, by typically an order of magnitude. We compared cross-sections calculated using the full CH3OH–He interaction potential, which is a function of the torsion angle, with the cross-sections computed for the staggered conformation, i.e. for a fixed value of the torsion angle. The agreement between these two sets of results improves with increasing magnitude of the cross-section. Accordingly, the use of previous results, for the rotational excitation of methanol by He and by H2, obtained for the staggered conformation, should not compromise the analysis of observations of methanol in the interstellar medium.

Keywords: molecular data; molecular processes; ISM: molecules; radio lines: ISM

Journal Article.  2997 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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