The physical interaction potential of gas atoms with single-crystal surfaces, determined from gas-surface diffraction experiments

A comprehensive survey and data collection of experimental results achieved from diffracting beams of light gases like H, D, ^3He, ^4He, and H₂ from single-crystal surfaces (alkali halides, oxides, and graphite) is given, and it is shown that gas-surface diffraction is a valuable tool to get detailed information on the physical gas-surface potential: (a) From comparison of diffracted beam intensities with calculations in a corrugated hardwall approximation the periodic structure of the interaction potential is obtained together with information on the atomic structure at the surface. (b) From bound-state resonance investigations one gets information on the different terms of the gas-surface potential in Fourier expansion v (r) =₆ v₆ (z) exp (iG): the achieved spectrum of binding energies {E₉} can be used to construct the main term v₀₀ (z), whereas observed splitting of degenerate bound states allows evaluation of the strength of the periodic terms v₆ (z). (c) from E₉ levels near the dissociation limit the constant C₃ of gas-surface long-range dispersion attraction can be determined. Finally, regarding the experimental results on C₃ and the potential well depth D, two semiempirical rules are established: C₃=K₂ (-1) (+1) and D=K₃ (-1) (+1). These rules allow the calculation of C₃ and D from the static electric polarizability of the atom, the optical dielectric constant of the solid, and the system-independent constants K₂, K₃ given in the text. Calculated values of D for several gas-surface systems are given in a table.