Desorption of neutrals by temporary ionization of atoms and molecules physisorbed on a metal surface: Quantum-mechanical versus classical approach

The quantum theory of desorption by temporary ionization of atoms or molecules physisorbed on a metal surface is developed by the use of Feshbach projection-operator formalism of multichannel scattering. The basic mechanism, as described by Antoniewicz, is an ionization to a more strongly bound state, acceleration towards the surface, and reneutralization after sufficient kinetic energy has been acquired to overcome the van der Waals attraction after reflection at the surface. The results of the quantum theory are compared with the results of an earlier classical approach via numerical comparison of kinetic-energy distributions of desorbed neutral particles computed in both theories for He and ${\mathrm{N}}_2$O physisorbed on W and Ru(001), respectively. The differences are large for the former and smaller, but still very obvious, for the latter system, particularly for strongly-position-dependent neutralization rates.