Wave packet calculations for H2+H2 collisions: isotopic substitution effects

Abstract

Isotopic substitution effects for H2(v 1 = high)+H2(v 2 = low) collisions are studied by means of time-dependent wave packet calculations. A three degree-of-freedom reduced dimensionality model was employed, which can account for collision-induced dissociation as well as for four centre exchange processes, for reactants in selected vibrational states. Mass effects are studied in two ways: by substituting the collider H2(v 2=low) by D2 in the same vibrational state, or by substituting the target H2(v 1 = high) by D2 in a state with a similar vibrational energy. For the collider in its ground vibrational state, we have found that four centre probability profiles are quite similar but, conversely, thresholds for dissociation probabilities are quite different for the different mass combinations. The H2(v 1 = high)+D2(v 2 = low) combination was found to be the most effective one for the dissociation process. In addition, the process of dissociation of the vibrationally cold diatom was found to be quite important in H2(v 1=14) + D2(v 2=1,2) collisions. These effects are analysed by means of plots of the potential energy surface using mass-scaled coordinates.