title: Multiple pathways of dissociative attachment: CH3Br on Si(100)-2×1.
abstract: We describe the dissociative attachment (DA) of methyl bromide to form chemisorbed CH(3) and Br on a Si(100)-2×1 surface at 270 K. The patterns of DA were studied experimentally by ultra-high vacuum scanning tunneling microscopy (STM) and interpreted by ab initio theory. The parent molecules were found to dissociate thermally by breaking the C-Br bond, attaching the resulting fragments CH(3) and Br at adjacent Si-atom sites. The observed DA resulted in three distinct attachment geometries: inter-row (IR, 88%), inter-dimer (ID, 11%), and on-dimer (OD, 1%). Ab initio computation agreed in predicting these three DA reaction pathways, with yields decreasing down the series, in accord with experiment. The three computed physisorption geometries, each of which correlated with a preferred outcome, IR, ID, or OD, exhibited similar heats of adsorption, the choice of pathway being governed by the energy barriers to DA chemisorption predicted to increase along the series: E(IR) = 0.48 eV, E(ID) = 0.57 eV, and E(OD) = 0.63 eV.
authors.affiliation: Department of Chemistry and Institute of Optical Sciences, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Ting Bin
authors.initials: TB
authors.lastname: Lim
authors.forename: Iain R
authors.initials: IR
authors.lastname: McNab
authors.forename: John C
authors.initials: JC
authors.lastname: Polanyi
authors.forename: Hong
authors.initials: H
authors.lastname: Guo
authors.forename: Wei
authors.initials: W
authors.lastname: Ji
mesh_terms: D006842:Hydrocarbons, Brominated / Q000737:chemistry*; D008958:Models, Molecular; D011789:Quantum Theory; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D006842:Hydrocarbons, Brominated; C005218:methyl bromide; D012825:Silicon