Collision‐induced Dissociation of Molecular Hydrogen at Low Densities

Quasi-classical trajectory studies have been carried out on a chemically accurate H 4 potential-energy surface for H 2 + H 2 interactions to obtain cross sections for collision-induced dissociation (CID) from the H 2 (0, 0) ground vibration-rotation state. This is an important channel for dissociation, particularly in a low-density gas. These results are compared with corresponding calculations for the H + H 2 and He + H 2 systems. Collisions with the H 2 (0, 0) collision partner do not show the same dynamical elevation of threshold for CID seen previously for collisions with He. Despite the energetic threshold, H 2 (0, 0) is a much less effective collision partner in promoting CID than is H. Thermal rate coefficients for CID from the ground state are evaluated and compared to earlier approximations. A comparison with electron impact dissociation is also made.