IMPULSIVE EXCITATION OF FECP(2)(-INDUCED DISSOCIATION AT ORGANIC MULTILAYERS() AND SIME(3)(+) DURING SURFACE)

These experiments scattered 20-90 eV FeCp(2)(+) (Cp=cyclopentadiene) a nd SiMe(3)(+) ions off multilayers of propylene (C3H6), hexafluoroprop ylene (C3F6), and tetrachloroethylene (C2Cl4) adsorbed on Ni(111). The ion internal energies following the surface collisions were estimated from the relative fragment ion intensities. The kinetic to internal e nergy transfer efficiencies varied as follows: C2Cl4 (similar to 15%)g reater than or equal to C3F6 (similar to 14%) > C3H6 (similar to 10%). The scattered ion kinetic energies were less than 10% of the incident ion energy and did not depend upon the incident ion energy or angles, but did depend upon the chemical identity of the multilayer. The expe rimental data was analyzed in terms of a three step model of surface-i nduced dissociation which was previously described to explain the scat tering of Cr(CO)(6)(+) off organic monolayers [J. A. Burroughs. S, B. Wainhaus, and L. Hanley, J. Phys, Chem. 98, 10 913 (1994)]. Impulsive excitation is the first step of this model and it semiquantitatively p redicted (within a factor of 2) the experimental kinetic to internal e nergy transfer efficiencies. Impulsive excitation was estimated to occ ur within 10-35 fs of the initial ion impact. Inelastic scattering and unimolecular dissociation were the latter steps of this model. Both F eCp(2)(+) and SiMe(3)(+) underwent the inelastic scattering step, with the surface dissipating similar to 70% of the incident ion kinetic en ergy. Unlike the unimolecular dissociation observed for Cr(CO)(6)(+) s cattering off organic monolayers, both FeCp(2)(+) and SiMe(3)(+) were crudely estimated to dissociate at the surface within 3 ps of the init ial ion impact. (C) 1995 American Institute of Physics.