THE INTERACTION OF UNSATURATED HYDROCARBONS WITH MULTIMETAL SITES IN TRANSITION METAL COMPLEXES AND ON SURFACES (ETHYLENE, ACETYLENE, PLATINUM, COBALT).

摘要

The nature of the interaction of acetylene and ethylene with single crystal transition metal surfaces has been investigated with photoelectron spectroscopy using three different approaches. Firstly, angle resolved photoemission using synchrotron radiation has been employed in the characterization of the high temperature phase of ethylene and acetylene on Pt(111). Exploitation of the plane polarized nature of synchrotron radiation and the resulting symmetry selection rules has determined that the ethylidyne structure is the most likely. Secondly, unpolarized He(II) radiation was used to analyze the bonding and thermal decomposition of ethylene on Co(0001). The geometry of the surface bound ethylene molecule was determined from the calculations of Demuth and the methodology of Felter and Weinberg. On Co(0001), ethylene decomposes directly to carbon and hydrogen and does not pass through an acetylene intermediate. Because of this, and the kinetic model for ethylene chemisorption on Pt(100) of Fischer and Keleman, it is proposed that ethylene occupies an on-top site with each of the hydrogens interacting with a unique surface cobalt atom. Thirdly, the nature of the interaction of acetylene on Co(0001) is investigated by applying the cluster-surface analogy to that system. Photoemission spectra of the series; Co(,2)(CO)(,6)(RCCR'), R,R' = -CH(,3), -H or -CH(,3), were collected using x-ray and ultraviolet radiation. It was determined that the peak assigned to the metal-carbon bonding interaction broadened with increasing R-group electronegativity. Since this observation was shown to be indicative of the nature of the hydrocarbon-metal bond in the complex, the corresponding surface data was collected where a similar trend was observed. This was interpreted to indicate that the surface and metal complex interactions were similar in nature. A review of hydrocarbon chemisorption with 108 references is also presented.