FT-IRAS OF ADSORBED ALKOXIDES - FLUORINATED ETHOXIDES ON CU(111)

Fourier transform infrared reflection absorption spectra (FT-IRAS) of a set of fluorinated ethoxides (CFnH3-nCH2OH, n = 0-3) on the Cu(lll) surface have been obtained. The decomposition reactions of adsorbed mo no-, di-, and trifluoroethoxide to gaseous fluoroaldehydes exhibit dif ferent reaction kinetics, as previously reported, and the reaction of trifluoroethoxide-d(2) (CF3CD2O-Cu(111)) exhibits a primary isotope ef fect. Quantitative measurements of the absorption intensities of CF3CH 2O(ad) and CF3CH2OH allowed determination of the orientation of the ad sorbed trifluoroethoxide. FT-IRAS results indicate that the orientatio n of trifluoroethoxide is different than that of ethoxide. Ethoxide on the Cu(lll) surface has the C-C bond tilted 70 +/- 2 degrees from the surface normal while in trifluoroethoxide the C-C bond is oriented 50 +/- 5 degrees from the surface normal. In both species the plane of t he molecule defined by the C-C-O atoms is tilted toward the surface. T his tilt between the plane of the molecule and the plane of the surfac e normal is 17 +/- 2 degrees for ethoxide and 20 +/- 11 degrees for tr ifluorethoxide. These results indicate that the effect of fluorination of the methyl end group is to tilt it away from the surface.