Rotational excitation of methylidynium (CH+) by a helium atom at high temperature

Free access article

Issue		A&A Volume 507, Number 2, November IV 2009


Page(s)		1083 - 1086
Section		Atomic, molecular, and nuclear data
DOI		http://dx.doi.org/10.1051/0004-6361/200912663
Published online		17 September 2009

A&A 507, 1083-1086 (2009)
DOI: 10.1051/0004-6361/200912663

Rotational excitation of methylidynium (CH⁺) by a helium atom at high temperature

K. Hammami¹, L. C. Owono Owono^{2, 3}, and P. Stäuber^{4, 5}

¹ Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Département de Physique, Faculté des Sciences, France
e-mail: hammami283@yahoo.fr
² Université Tunis El Manar, Campus Universitaire, 1060 Tunis, Tunisia
³ Department of Physics, Advanced Teachers Training College, University of Yaounde I, PO Box 47, Yaounde, Cameroon
⁴ Centre for Atomic Molecular Physics and Quantum Optics, Faculty of Science, University of Douala, PO Box 8580, Douala, Cameroon
⁵ Institute for Astronomy, ETH Zurich, 8093 Zurich, Switzerland
e-mail: pascalst@astro.phys.ethz.ch

Received 9 June 2009 / Accepted 26 August 2009

Abstract
Context. The Herschel Space Observatory with its high-resolution instrument HIFI on board will observe the CH⁺ $1\rightarrow0$ and $2\rightarrow1$ rotational transitions in a wide range of gas temperatures up to 1000 K. Collisional parameters for such temperatures are thus welcome.
Aims. We aim to obtain accurate rate coefficients for the collisional excitation of CH⁺ by He for high gas temperatures.
Methods. The ab initio coupled-cluster [CCSD(T)] approximation was used to compute the interaction potential energy. Cross sections are then derived in the close coupling (CC) approach and rate coefficients inferred by averaging these cross sections over a Maxwell-Boltzmann distribution of kinetic energies.
Results. Cross sections are calculated up to $10\,000~\mathrm{cm^{-1}}$ for J ranging from 0 to 10. Rate coefficients are obtained at high temperatures up to 2000 K.

Key words: astrochemistry -- molecular data -- radiative transfer -- ISM: molecules

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