IMPULSIVE EXCITATION OF CR(CO)(6)(-INDUCED DISSOCIATION AT ORGANIC MONOLAYERS() DURING SURFACE)

20 to 120 eV Cr(CO)(6)(+) ions are scattered off heptafluorobutyrate a nd hexanethiolate monolayers adsorbed on Ag(111), and the fragment ion s formed by surface-induced dissociation (SID) are detected. The relat ive fragment ion intensities are monitored to produce SID breakdown cu rves, which are subsequently compared with threshold photoelectron pho toion coincidence (TPEPICO) data to estimate the internal energy of Cr (CO)(6)(+) following the surface collision. The kinetic to internal en ergy transfer is more efficient for the fluorocarbon than the hydrocar bon monolayer. The scattered ion velocities are centered near 3000, 40 00, and 5000 m/s for initial Cr(CO)(6)(+) velocities of 5100, 7800, an d 9800 m/s, respectively (30, 70, and 110 eV). A three-step mechanism for SID is proposed in which ions initially undergo impulsive excitati on by collision with the surface, inelastically reflect off the surfac e, and finally dissociate unimolecular. The experimental kinetic to in ternal energy efficiencies are fit to an impulsive excitation model wh ich quantitatively duplicates the dependence on both the initial kinet ic energy and the effective mass of the adsorbate, at the lower collis ion energies.