Dynamics of triatomic photodissociation in the interaction representation. I. Methodology

This paper presents a new, quantum mechanical, time dependent approach to the photodissociation of triatomic molecules in Jacobi coordinates. The algorithm is based on a nested interaction representation, designed to make the representation of the time evolving wave packet as compact as possible. The new equations of motion are solved numerically using a synthesis of grid techniques: the fast Fourier transform (FFT) method is used in Cartesian-like coordinates, and the discrete variable representation (DVR) method in the angular or bending coordinate. A variant on the short iterative Lanczos (SIL) procedure is used for the temporal propagation of the wave packet. Rotational state distributions obtained from this new algorithm are presented for the single surface photodissociation of ClCN and for the two surface photodissociation of ICN. The ClCN results are in good agreement with the semiclassical results of Barts and Halpern [J. Phys. Chem. 93, 7346 (1989)] and in excellent agreement with the time independent quantum results of Schinke [J. Chem. Phys. 92, 2397 (1990)]. Rotational state distributions for the two electronic surface photodissociation of ICN are in good agreement with the time independent quantum results of Guo and Schatz [J. Chem. Phys. 92, 1634 (1990)] and illustrate the flexibility of the method for dealing with nonadiabatic processes. The numerical efficiency of the method is comparable with standard time independent techniques, but has the attractive feature of yielding final state distributions at all energies from a single wave packet propagation.