Journal Article

Fine and hyperfine excitation of C<sub>2</sub>H by collisions with He at low temperature

A. Spielfiedel, N. Feautrier, F. Najar, D. Ben Abdallah, F. Dayou, M. L. Senent and F. Lique

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 3, pages 1891-1896
Published in print April 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI:
Fine and hyperfine excitation of C2H by collisions with He at low temperature

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Modelling of molecular emission from interstellar clouds requires the calculation of rate coefficients for excitation by collisions with the most abundant species. From a new, highly correlated, two-dimensional potential energy surface, rotational excitation of the C2H(X2Σ+) molecule by collision with He is investigated. State-to-state collisional excitation cross-sections between the 25 first fine structure levels of C2H are calculated for energies up to 800 cm−1 which yields after thermal averaging rate coefficients up to T= 100 K. The exact spin splitting of the energy levels is taken into account. The recoupling technique introduced by Alexander & Dagdigian allows us to deduce the corresponding temperature-dependent hyperfine state-to-state rate coefficients. Propensity rules are discussed.

Keywords: line: formation – molecular data; molecular processes; scattering; ISM: molecules

Journal Article.  3874 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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