Dynamical atom/surface effects: Quantum mechanical scattering and desorption

Desorption and scattering of a helium atom from dynamic surfaces are studied using a generalized Langevin equation formalism for the bulk solid and time dependent quantum mechanical propagation of the helium. The motion of the bulk solid enters the Schrödinger equation as a time dependent potential coupling the solid surface to the atom. The propagation of the atomic wave packet is then followed in coordinate space using a Fourier transform technique to evaluate the kinetic energy operator. An attenuating grid is used to remove the wave packet in the asymptotic region thus permitting stable calculations for long duration times. Rates for one dimensional desorption from tungsten as a function of temperature are computed which display a change in mechanism. Three dimensional scattering from platinum at two temperatures shows significant nonspecular amplitude. These results indicate the utility of this time dependent technique.