Kinetic energy distribution of H(1s) from H2 X 1Σ+g-a 3Σ+g excitation and lifetimes and transition probabilities of a 3Σ+g(v, J)

Abstract

Dissociative excitation of molecular hydrogen plays an important role in the heating of outer planet upper thermospheres. This paper addresses the role of one of the triplet states involved in the process. H2 excited to the a 3Σ+g state, or higher triplet-ungerade states, is dissociated via the a 3Σ +g-b 3Σ+u continuum. The kinetic energy distribution of H(1s) produced from direct X 1Σ+g-a 3Σ+g(v, J) excitation by electrons is investigated by an accurate theoretical evaluation of spontaneous transition probabilities of the a 3Σ+g(v, J)-b 3Σ +u continuum transition. It is shown that the X 1Σ+g(0)-a 3Σ +g(v, J) excitation primarily produces H(1s) atoms with kinetic energies lower than 2 eV. In addition to the continuum a 3Σ+g(v, J)-b 3Σ +u transition probabilities, spontaneous emission lifetimes of the a 3Σ+g(v, J) (v = 0-20, J ≤ 14) levels have been calculated by considering both the a 3Σ+g-b 3Σ+u and a 3Σ+g-c 3Πu transitions. The calculated lifetimes show a moderately strong rotational dependence, and the lifetimes for the J = 0 rotational level of the low v levels agree well with previous calculations and experimental measurements. Calculations of the a 3Σ+g-b 3Σ+u continuum emission spectra from electron impact X 1Σ+g-a 3Σ+g excitation are included. © 2010. The American Astronomical Society. All rights reserved.