A comparative study of the low energy HD plus o-/p-H-2 rotational excitation/de-excitation collisions and elastic scattering

Abstract

The Diep and Johnson (DJ) H-2-H-2 potential energy surface (PES) obtained from the first principles [P. Diep, K. Johnson, J. Chem. Phys. 113, 3480 (2000); 114, 222 (2000)], has been adjusted through appropriate rotation of the three-dimensional coordinate system and applied to low-temperature (T < 300 K) HD+o-/p-H-2 collisions of astrophysical interest. A non-reactive quantum mechanical close-coupling method is used to carry out the computation for the total rotational state-to-state cross sections sigma(j1j2)-> j(1)'j(2)'(epsilon) and corresponding thermal rate coefficients k(j1j2)-> j(1)'j(2)'(T). A rather satisfactory agreement has been obtained between our results computed with the modified DJ PES and with the newer H-4 PES [A. I. Boothroyd, P. G. Martin, W. J. Keogh, M. J. Peterson, J. Chem. Phys. 116, 666 (2002)], which is also applied in this work. A comparative study with previous results is presented and discussed. Significant differences have been obtained for few specific rotational transitions in the H-2/HD molecules between our results and previous calculations. The low temperature data for k(j1j2)-> j(1)'j(2)'(T) calculated in this work can be used in a future application such as a new computation of the HD cooling function of primordial gas, which is important in the astrophysics of the early Universe. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.3699203]