Collision Model of `Fall-Off´ in Recombination Reactions

Assuming random, multiple collisions the `fall-off´ problem in chemical recombination reactions is reconsidered. Following this approximative model the `fall-off´ from third order reactions at low pressure to second order reactions at high pressure appears in a simple way as a consequence of the collision time considered as the lifetime of the unstable van der Waals complex formed initially in the recombination mechanism. Comparisons are presented for results from the `fall-off´ following the Lindemann type mechanism, and of the method of Troe, Gilbert