Orientation of Physisorbed Fluoropropenes on Cu(111)

Fourier transform infrared reflection absorption spectra (FT-IRAS) have been obtained for adsorbed monolayers of propene and a set of fluorinated propenes (CFH 2 CH CH 2, CF 3 CH CH 2, and CF 3 CF CF 2 ) on the Cu(111) surface. These species interact weakly with the copper surface. The FT-IRAS spectra indicate that the molecules lie flat with the plane of the molecule defined by the C C C atoms essentially parallel to the surface regardless of the degree of fluorination. Quantitative analysis of the orientation of hexafluoropropene determines the tilt of the molecular plane with respect to the surface to be 11°. The results for propene indicate a molecular tilt of 20°. Where the ν(C C) mode can be identified in the spectra of the adsorbed molecules, there is no perturbation of its frequency, which indicates that there is little backdonation between the metal and the π* orbital of the propene.