Ion-dipole fragmentations

Abstract

We describe a rotationally adiabatic approach for calculating kinetic energy release distributions for ion-dipole fragmentations which proceed through an orbiting transition state. The system is assumed to remain in the same rotational quantum state in the long range region during its passage from transition state to products. The rotational state specific behaviour under the influence of the anisotropic ion-dipole potential is accounted for by assuming that the energy of a rotational quantum state can be described approximately by the corresponding rotationally adiabatic potential energy curve. The rotational adiabats are calculated using a quantum scattering method involving the centrifugal sudden approximation. The internal modes of the reactant undergoing dissociation are considered to be strongly coupled. The kinetic energy release distribution for the H₃O⁺/H₂O system is calculated and found to agree well with the experimental spectrum obtained by Bowers et al. using mass-analysed ion kinetic energy spectroscopy. More detailed comparison with experiment is necessary, however, to test conclusively the validity of the assumption of long range rotational adiabaticity.