Fine and hyperfine excitation of C₂H by collisions with He at low temperature

Author： Spielfiedel A. Feautrier N. Najar F. Ben Abdallah D. Dayou F. Senent M. L. Lique F.

ISSN： 0035-8711

Source： Monthly Notices of the Royal Astronomical Society, Vol.421, Iss.3, 2012-04, pp. : 1891-1896

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Abstract

ABSTRACTModelling 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.