AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuA

Paper SS1-TuA8
Radical Rearrangement as a Probe of Partial Oxidation Mechanisms: Reaction of (Bromomethyl)cyclopropane on Oxygen-Covered Mo(110)

Tuesday, October 3, 2000, 4:20 pm, Room 208

Session: Mechanisms and Control of Surface Reactions
Presenter: J.A. Levinson, Harvard University
Authors: J.A. Levinson, Harvard University
M.A. Sheehy, Harvard University
L.J. Deiner, Harvard University
I. Kretzschmar, Harvard University
C.M. Friend, Harvard University
Correspondent: Click to Email
Rearrangement reactions were used to study the transient intermediates formed during partial oxidation on oxygen-covered (0.75 ML) Mo(110) surfaces using (bromomethyl)cyclopropane. Using temperature programmed reaction spectroscopy, a competition between desorption and reaction was observed, with 1,3-butadiene, butene, ethylene, water, and dihydrogen as reaction products; these were evolved between 450 and 600 K. No cyclic or three-carbon species were observed in the mass spectroscopic data. Two linear analogues, 4-bromo-1-butene and 3-buten-1-ol, were also studied and produced similar product spectra. Coadsorption experiments with deuterated species revealed that the hydrogen incorporated into butene and ethylene arises at the time of reaction from the reaction intermediate. Mass spectra indicated that there may be both alkyl and alkoxide species at the surface for the Br-containing compounds, as the hydrocarbon products are evolved at two temperatures. X-ray photoelectron spectroscopy experiments are in progress to determine the surface bonding and the temperature of C-Br bond scission. Fourier transform infrared spectroscopy was used to determine conformational and structural changes in the surface intermediates as a function of temperature. For (bromomethyl)cyclopropane, a double bond appears near 400 K. These data imply that a ring-opened intermediate forms following C-Br bond scission, which is then followed by H-elimination or incorporation. The use of isotopically labeled oxygen on Mo(110) revealed that the alkoxide species for the Br-compounds bind through surface oxygen, whereas the alcohol binds through its original hydroxyl group. Lowering reactant coverage reduces butene and butadiene formation and favors ethylene production. Variation of oxygen coverage from saturation to clean Mo(110) surfaces causes selective product formation to convert to non-selective decomposition.