Stimulated desorption of neutrals: quantum effects in the Antoniewicz model

Abstract

The quantum theory of stimulated desorption of a neutral van der Waals bound adsorbate via excitation of an ionized intermediate state is studied. The asymmetric decay introduced by quantum motion in a strongly varying imaginary potential leads to a different dependence of coordinate and velocity on time. The position xcrit which has to be reached, so that the adsorbate has enough kinetic energy to be desorbed is shifted. Both these effects have a tendency to cancel each other. On the other hand the broadening of the wave packet leads to a corresponding broadening of the energy distribution and a certain spread of possible xcrit values. The final result is an increase of the intensity of neutrals combined with a shift of the peak of the intensity distribution to higher energies. The agreement with experiment is partly better, partly worse as compared to classical theory. To obtain full agreement one probably has to use a better adjustment of the real part of the excited state potential: A simple superposition of groundstate plus image potential does not seem to be good enough.