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

Abstract

<i>Context. <i/>The <i>Herschel Space Observatory<i/> with its high-resolution instrument HIFI on board will observe the CH<sup>+<sup/> and rotational transitions in a wide range of gas temperatures up to 1000 K. Collisional parameters for such temperatures are thus welcome.<i>Aims. <i/>We aim to obtain accurate rate coefficients for the collisional excitation of CH<sup>+<sup/> by He for high gas temperatures.<i>Methods. <i/>The ab initio <i>coupled-cluster<i/> [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.<i>Results. <i/>Cross sections are calculated up to for <i>J<i/> ranging from 0 to 10. Rate coefficients are obtained at high temperatures up to .