State resolved rotational excitation in HD+D2 collisions. II. Angular dependence of 0→2 transitions

Abstract

Time‐of‐flight spectra for the scattering of HD molecules from D₂ molecules have been measured at a collision energy of E=70.3 meV over a range of center‐of‐mass scattering angles from 45° to 158°. The spectra reveal clearly resolved transitions at the energy loss ΔE=33 meV which corresponds to 0→2 transitions of HD and the double transition 0→1 of HD and 0→2 of D₂. The differential cross sections derived from these spectra increase with increasing scattering angle from 1.7% to 34.7% of the elastic cross section. The pure 0→2 transition of D₂ which only needs 22 meV to be induced could not be detected within our experimental sensitivity of 0.02 Ų/sr. Closed coupled calculations based on the ab initio potential surface of Meyer and Schaefer show that this result can be explained by the different coupling terms which are responsible for these transitions. In contrast to the 0→1 transition the 0→2 transition of HD proved to be sensitive to the anisotropic part of the interaction potential for the homonuclear system. The comparison of experimental and calculated cross sections for the ab initio potential of Meyer and Schaefer reveals discrepancies for the 0→1 transition of HD, but shows agreement for the 0→2 transition of HD at intermediate angles.