Photodissociation dynamics of A state ammonia molecules III. A three-dimensional time-dependent calculation using ab initio potential energy surfaces

Abstract

The dissociation dynamics for NH3(A) → H + NH2([Xtilde]) have been calculated using time-dependent quantum theory and an ab initio potential in the three dimensions of NH stretching, the out-of-plane motion and HNH bending. These calculations use a Hamiltonian for a combination of internal coordinates for NH2 and Jacobi coordinates for the relative motion of the H atom. Inclusion of HNH bending removes most of the gross inaccuracies present in earlier two-dimensional calculations. The calculated dissociation rates are, in general, lower than observed experimentally, indicating that the effective potential barrier to dissociation is too high. This is attributed to the influence of neglected vibrations. Excited state vibronic resonance energies, resulting product-state population distributions and state-dependent product recoil anisotropy factors compare favourably with experiment, permitting a detailed interpretation of the dissociation dynamics. Dissociation through the 00 and 21 levels of the A state pro...