A reconsideration of the theory of capture cross-sections for ion/molecule reactions and a total energy and angular momentum conserved average charge—dipole interaction theory (teams)

Abstract

Five capture-collision approaches commonly used to treat ion/molecule reactions, including Langevin theory (LT), the locked-dipole approximation (LD), Barker—Ridge theory (BR), the average dipole orientation theory (ADO), and the angular momentum conserved ADO theory (AADO), are examined in detail. Various inconsistencies are found in the theoretical developments of all but the first of these. Within the framework of an average ion-dipole interact potential, the principal developments of these theories are generalized and reformulated to account properly for the conservation of both total energy total angular momentum. This general approach, termed TEAMS, removes all obvious shortcomings in the existing capture collision theories, but retains t usual averaging process employed to obtain the averaged ion—dipole potential. Numerical predictions of the capture rate constants for all the above-m models are compared for the collision pair H + and HCN over a wide range of initial conditions. The results of these computations serve to elucidate the dependence of capture collision rates on the dipole rotational temperature and the relative collisional energy of the interacting pair. The theoretical validity and the practical applicability of the theories in making comparisons with experim measured reaction rate constants are also discussed.