Spin-orbit quenching of the C + ( 2 P ) ion by collisions with para - and ortho -H 2

François Lique (1) , Ghofran Werfelli , Philippe Halvick (2) , Thierry Stoecklin (2) , Alexandre Faure (3) , Laurent Wiesenfeld (3) , Paul Dagdigian

1 LOMC - Laboratoire Ondes et Milieux Complexes
2 ISM - Institut des Sciences Moléculaires
3 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

Spin-orbit (de-)excitation of C+(2P) by collisions with H2, a key process for astrochemistry, is investigated. Quantum-mechanical calculations of collisions between C+ ions and para- and ortho-H2 have been performed in order to determine the cross section for the C+ 2P3/2 → 2P1/2 fine-structure transition at low and intermediate energies. The calculation are based on new ab initio potential energy surfaces obtained using the multireference configuration interaction method. Corresponding rate coefficients were obtained for temperatures ranging from 5 to 500 K. These rate coefficients are compared to previous estimations, and their impact is assessed through radiative transfer computation. They are found to increase the flux of the 2P3/2 → 2P1/2 line at 158 μm by up to 30% for typical diffuse interstellar cloud conditions.

Domaines: Physique [physics]

François Lique, Ghofran Werfelli, Philippe Halvick, Thierry Stoecklin, Alexandre Faure, et al.. Spin-orbit quenching of the C + ( 2 P ) ion by collisions with para - and ortho -H 2. Journal of Chemical Physics, 2013, 138 (20), pp.204314. ⟨10.1063/1.4807311⟩. ⟨hal-03047305⟩