SPECULAR REFLECTION OF HELIUM AND HYDROGEN MOLECULAR-BEAMS FROM THE (111) PLANE OF SILVER

The Debye-Waller (DW) factor in the specular reflection intensity of He and H2 molecular beams from the Ag (111) plane has been studied experimentally and theoretically. A new expression for the DW factor corrected for a stationary part of the gas-surface interaction potential is derived kinematically and semi-classically by the use of a Morse potential. An analysis of the experimental data through the above DW factor yields a surface Debye temperature of 251 ± 20 K, which is unusually high, and potential depths of 1.5 ± 1.0 meV for He and 6.4 ± 2.9 meV for H2, which seem slightly too small. These results are discussed on the basis of the nature of gas-surface interactions and in comparison with the results deduced from the conventional DW factor corrected for a constant attractive potential depth. © 1979.