A three-dimensional wavepacket study on photodissociation dynamics of methyl iodide

Abstract

The photodissociation dynamics of methyl iodide is investigated on a three-dimensional grid using a time-dependent quantum mechanical method. Two electronic states which correlate with I and I * fragments are explicitly included in the calculation and their potential energy functions as well as their coupling are adapted from a recent ab initio calculation by Morokuma and co-workers. The dynamically active dimensions include (1) the dissociation coordinate, (2) the umbrella bend of the methyl group which is treated as a stretch between a hypothetic atom (H 3) and the carbon atom; and (3) the H 3CI bend. The discrete variable representation is used to describe the dynamics in the bending coordinate θ while the other two degrees of freedom are treated by a FFT based approach. The time propagation of the wavepacket is carried out using the Chebychev expansion of the time propagator and the grid in the translational coordinate space is shifted during the propagation to avoid reflection at the end of the grid. Vibrational and rotational distributions for the CH 3 fragment and I * yields are calculated for several photon frequencies. The three-dimensional quantum mechanical results are compared with experimental data and an earlier quasi-classical calculation based on the same potential energy surfaces.