Fragmentation of molecules sliding along surfaces in the speed range abovethermal and below Bohr velocity

A theoretical model and experimental time-of-flight mass spectrometric data for the fragmentation of molecules grazing along surfaces at velocities v = 10(5)-10(6) cm/s are presented. The effect of enhanced surface-induced di ssociation at grazing incidence (GI-SID) is shown for hexadecylpyridine ion s. The velocity dependence of the GI-SID fragmentation probability is studi ed in experiments with adduct ions of cyclodextrin derivatives. Surfaces us ed in the various collision experiments are aluminum oxide, gold, and a liq uid film of perfluorinated polyether. In the theoretical model of the GI-SI D effect we consider polyatomic molecules with substructures consisting of chains of identical biatomic dipoles. Because of the interaction with the p eriodic Coulomb field of the surface, collective vibrational excitations (e xcimols) are induced in these chains. Energy accumulation of several excimo ls and a subsequent energy transfer to a trap bond can induce its dissociat ion. An analytical expression for the velocity dependent GI-SID fragmentati on probability is given, which is in good agreement with the experimental d ata. (C) 1999 American Society for Mass Spectrometry.