Vibrationally inelastic collisions of H+D2: a comparison of quantum mechanical, quasiclassical, and experimental results.

A detailed comparison of quantum mechanical (QM) and quasiclassical trajectory (QCT) integral and differential cross sections (DCSs) as well as opacity functions is presented in this work for the vibrationally inelastic collisions of H+D(2)(v=0,j=0)-->H+D(2)(v(')=3,j(')) at 1.72 eV collision energy. These results are also compared with the experimental differential cross sections by Greaves et al. [Nature (London) 454, 88 (2008)]. The agreement between QCT and QM results is fairly good but some differences are appreciable, and it is shown that the experimental results are in a somewhat better agreement with the calculated QM DCS. The present results and their analysis confirm that the vibrational excitation takes place by elongation of the D-D bond in a "tug-of-war" mechanism, where the incoming H atom and one of the D atoms compete for the formation of a bond with the other D atom, as proposed by Greaves et al. It is also found that these collisions may give rise to the formation of short-lived collision complexes (tau(coll)=35-50 fs) that can be traced back to the presence of relatively deep wells in the potential surface when the original D-D bond is stretched. The analysis of the trajectories into v(')=3 reveals that most of them cross at least twice the reaction barrier via a recrossing mechanism.