Dissociative resonance activation of cyclopropane monolayers on copper: Evidence for CH and CC bond scission

Abstract

Energy selective electron beam modification of cyclopropane on Cu(110) and Cu(111) single crystal surfaces was performed using the electron beam intrinsic to a high resolution electron energy loss (HREELS) spectrometer. Vibrational spectra of the resulting adsorbed dissociation fragments were recorded using the same HREELS spectrometer. Electron irradiation in the range 10-18 eV of weakly adsorbed cyclopropane was found to lead to the formation of chemisorbed dissociation fragments. HREELS and complementary thermal desorption data were used to identify the chemisorbed products as metallacyclobutane and cyclopropyl groups. The formation of these two surface species implies the existence of two dissociation channels involving CC and CH bond scission, respectively. Variations in the cross section for electron induced modification indicates the presence of a dissociative attachment resonance centered at approximately 10 eV. Cyclopropyl formation and ring opening of cyclopropane at 10 eV are attributed to competition between two decay channels of a core-excited resonance. The cross section for metallacyclobutane formation, at 10 eV, was evaluated to be roughly 0.8×10-17 cm2. The ratio of cyclopropyl to metallacyclobutane surface species, formed at 10 eV, was found to be 4:1. © 1997 American Institute of Physics.