ROTATIONAL COOLING AND HEATING IN ACTIVATED ADSORPTION-DESORPTION FOR D2/CU(111)

We consider a simple model for studying the rotational dynamics in a dissociative adsorption process (D2 at a Cu(111) surface). The experimentally detected decrease of the sticking coefficient with the initial rotational state j at low j and its increase at high j are accounted for. While the first effect is due to a dynamical reorientation of the molecule the latter effect can be traced back to an elongation of the molecular bond during dissociation. Depending on the surface temperature either rotational cooling or heating in desorption is to be expected.