Angular momentum conservation in multichannel unimolecular reactions

A recently developed solution of the master equation for unimolecular and recombination reactions is extended to give new means for incorporating angular momentum (J) conservation in the fall‐off regime for multichannel reactions. The calculated pressure dependence of a typical multichannel unimolecular dissociation reaction (thermal dissociation of 1‐iodopropane) shows that if one of the channels has a transition state with a moment of inertia (I†) significantly different from that of the parent molecule (I) (e.g., a “simple‐fission” type), neglect of angular momentum conservation causes the predicted branching ratio to be grossly in error at lower pressures. Specifically, if I† > I the rate coefficient is underestimated whereas if I† < I the rate coefficient is overestimated.