THEORETICAL MODELING OF PHOTODISSOCIATION DYNAMICS OF CH3I ON MGO(001)

The 257 nm photodissociation dynamics of CH3I adsorbed on a MgO(001) s urface is studied using classical molecular dynamics method. The subst rate is modeled by a 6X6X3 slab of movable ions surrounded by a semi-i nfinite array of static ions. A single adsorbate molecule is aligned w ith the surface normal, the methyl end pointed either toward or away f rom the substrate. The system is equilibrated by using a Monte Carlo m ethod to obtain the starting configuration. Fragment final state distr ibutions are calculated for kinetic energy, angle of departure, and ro vibrational states. Upon photodissociation of the adsorbate with the m ethyl end pointed toward the surface, the methyl fragments experienced vibrational cooling, in agreement with experimental results. Some rot ational excitation is predicted for fragments produced from the methyl down orientation. The kinetic energy distributions of both the methyl and iodine fragments are qualitatively similar to those obtained by e xperiment. The results are compared with those obtained by the same mo del for CH3I adsorbed on LiF(001). Trapping of iodine atoms by the sur face has also been investigated in this simulation. (C) 1995 American Institute of Physics.