Influence of angular momentum in the dissociation of NH +3

Abstract

Measurements of the fractional abundance of product ions and of the distributions of c.m. energy released into translation in the dissociation ²E NH⁺₃→ NH⁺₂+ H have been obtained as a function of system energy for state-selected ions using a photoelectron–photoion coincidence technique. The data are interpreted using a statistical-dynamical theory in which rotational and orbital angular-momentum states feature prominently. The model, which includes rigorous conservation of angular momentum, restrictions upon allowed states arising from the centrifugal barrier to dissociation and, optionally, the weighting of rotational levels by nuclear statistics, provides very good predictions of the experimental results including a newly observed phenomenon where the energy release initially diminishes with increasing system energy.

The results indicate that all initial rotational energy is available in the dissociation, subject only to the foregoing constraints, and although slight deviations from equiprobability of vibrational states are considered, randomization of energy seems to occur. The centrifugal barrier is shown to be a highly significant factor governing product energy distributions, particularly for high energies and high angular momentum states. The influence of nuclear statistics is less marked, though not negligible. The possibility of using such effects to identify product electronic species from the associated translational-energy releases is investigated.