QUANTUM DYNAMICS OF DISSOCIATIVE ADSORPTION OF H-2 AND D-2 - THE TIME-DEPENDENT WAVE-PACKET METHOD

A time-dependent quantum wave packet method was used to study the dyna mics of dissociative adsorption of H-2 and D-2 on a flat and static su rface. The molecule-surface interaction is described using a modified London-Eyring-Polanyi-Sato (LEPS) type potential for the H-2/Ni(100) s ystem. The three-dimensional (3-D) dissociation probabilities were cal culated for different initial rovibrational states as a function of in itial incident energies. Our results show that the dissociation of the diatomic rotational states whose quantum numbers satisfy j + m = odd is forbidden at low energies for the homonuclear H-2 and D-2 due to th e selection rule. The effect of the rotational orientation of diatoms on adsorption predicts that the in-plane rotation (m=j) is more favora ble for dissociation than the out-of-plane rotation (m = 0). Enhanced dissociation for vibrationally excited molecules and the significant e nhancement of the dissociation probability of H-2 when compared to D-2 were explained reasonably in terms of quantum mechanical zero-point e nergies, the tunneling effect and the reflection from an activation ba rrier.