ASSOCIATIVE DESORPTION OF HD AND D2 FROM A NI(100) SURFACE - ANGULAR AND VELOCITY DISTRIBUTIONS

A time of flight experiment was carried out to measure the angular and velocity distributions of HD and D2 thermally desorbing from Ni(100). The angular distributions can be described by a cos3theta dependence on polar angle. This is indicative of an activated mechanism of desorp tion. The angle-energy correlation shows a decrease of the average tra nslational energy of desorbing hydrogen molecules from [E] congruent-t o 2.9kT(s) close to the surface normal to [E] congruent-to 1.7kT(s) at 60-degrees off normal. A more detailed analysis comparing the data wi th those available in the literature shows that the results are compat ible with two desorption channels acting in parallel, one activated, t he other non-activated.