Dynamical simulations of the photodissociation of CH3Br on a LiF (001) surface.

The photodissociation dynamics of CH3Br adsorbed on LiF(001) is investigated using a classical molecular dynamics method. The adsorbate is modeled as a pseudodiatomic molecule and the LiF surface is represented by a cluster surrounded by static walls. All the particles involved are allowed to move in all three dimensions. It is found from Monte Carlo simulations that CH3Br binds to the LiF surface perpendicularly with a binding energy of approximately 0.3 eV. Both methyl up and Br up orientations of the adsorbate are found to be stable. The results from the dynamical simulations of the photodissociation process indicate that the experimental data for the CH3Br/LiF(001) photodissociation can only be explained on the basis of one dissociation channel open for the CH3Br photodissociation, in contrast to dual channels in the gas phase. When the methyl is up, its translational energy distribution resembles the corresponding gas phase result. In the case of methyl down and Br up, however, the dissociating methyl rebounds from the surface and collides with Br. With only a single collision, the kinetic energy of Br can be increased up to 1 eV, in agreement with experiment. [ABSTRACT FROM AUTHOR]