DETERMINATION OF QUANTUM-STATE-SPECIFIC GAS-SURFACE ENERGY-TRANSFER AND ADSORPTION PROBABILITIES AS A FUNCTION OF KINETIC-ENERGY

We describe a molecular beam technique for the determination of energy transfer and adsorption probabilities as a function of kinetic energy for specific quantum states of a molecule beam tailored to have a bro ad spread of energies. The beam is mechanically chopped into short pul ses at a large distance from the surface, so that velocity dispersion in the beam causes a spread in the arrival times at the surface. Time- of-flight distributions are then recorded using state-specific laser i onization detection at points immediately before and after the beam sc atters from the surface. Comparison of these two distributions then pr ovides information on the loss or pin of molecules in the chosen quant um state as a function of kinetic energy. The method is illustrated by application to the H-2(D2)/CU(111) system. In this case we have obser ved loss of incident flux due to dissociative chemisorption and pin of molecules in the first vibrationally excited state due to vibrational excitation of ground state molecules.