Unimolecular decomposition in a spherically symmetric potential

Unimolecular decompositions are considered where the interaction between the separating fragments can be described by a function solely of their radial separation. It is shown how previous treatments, confined to idealized models, can be generalized. Kinetic energy distributions and rate constants may be calculated accordingly when the angular momentum is low. Applications to evaporation from van der Waals molecules are noted. A limit to the interaction parameters is then found where these properties become ‘‘thermodynamic,’’ despite the absence of angular momentum. This result is used to obtain a general form for the effects of angular momentum on a rate constant. It reduces to traditional ideas in the hard-sphere limit.