Resonant dissociation of polyatomic surface molecules by hyperthermal ions

A theoretical approach is suggested for the fragmentation of polyatomic surface molecules by scattering of hyperthermal atomic and molecular ions. It is assumed that the surface molecules contain chains of identical diatomic valence groups as substructures. These chains can accumulate collective vibrational excitations (excimols), leading to subsequent nonstatistical molecular fragmentation. Low-energy incident ions at any incident angle are assumed to be reflected from the surface at atomic distances by the Coulomb potential, which acts for only a short period of time (10−13–10−12s). During this reflection period, the component of ion velocity normal to the surface is negligible, so ions move across the surface in a process that can be considered as a grazing collision. Analytical expressions are obtained for the fragmentation probabilities of surface molecules in grazing collisions with atomic and molecular ions. The probability of these processes strongly depends on the molecular structure and the incident ion velocity. The interaction between hyperthermal ions and molecules forming the outermost surface layer yields fragment molecules as a result of the mutual excitation processes. The experimental data on fragments generated from a fluorinated surface by action of incident ions are analyzed within the framework of the suggested model. Copyright © 2001 John Wiley & Sons, Ltd.