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 broad spread of energies. The beam is mechanically chopped into short pulses 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 ionization detection at points immediately before and after the beam scatters from the surface. Comparison of these two distributions then provides information on the loss or pin of molecules in the chosen quantum 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 observed 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.