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

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⁺ and 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 for J ranging from 0 to 10. Rate coefficients are obtained at high temperatures up to .