Kinetic energies of ${\mathrm{Ar}}^{+}$ ions desorbed by double photoionization at 100 eV from argon layers (from 2 to 20 monolayers) condensed on platinum are measured and compared with predicted values. Unexpected low kinetic energies are explained by a relaxed Coulomb repulsion mechanism. The weakness of the high-kinetic-energy ion signal is considered to be due to the noncrossing of the bound and repulsive potential-energy curves involved in the desorption model.

• Received 3 August 1993

DOI:https://doi.org/10.1103/PhysRevB.48.14529