Chemical reactions dominated by long-range intermolecular forces

Abstract

We describe a quantum-mechanical method for calculating cross-sections for chemical reactions dominated by long-range intermolecular forces. The technique involves a full close-coupling expansion of the scattering wavefunction, and boundary conditions are applied in the entrance channel of the reaction at a point inside the centrifugal barrier to the potential-energy surface. The theory is applied to the charge-dipole reactions He⁺+ HCl and e^–+ HI. The results are used to test the accuracy of several more approximate methods including a centrifugal sudden approximation and an adiabatic classical capture approximation. It is found that these approximations work well for the He⁺+ HCl reaction, but are not so accurate for the e^–+ HI reaction because of strong coriolis and quantum reflection effects that arise due to the very small mass of the electron. The results demonstrate that, in some cases, it will be straightforward and worthwhile to extend the quantum theories normally used for the reactions of atoms and ions to reactions involving electrons.