On the vibrational electron energy loss spectra of benzene chemisorbed on the (111) and (100) nickel faces

Abstract

The vibrational electron energy loss spectra of benzene chemisorbed, at room temperature (3 L exposure) on the Ni(111) and (100) faces, show the same loss peaks at 750, 845, 1115, 1325, 1425, 3025 cm −1 (540, 820, 1225, 1365 and 2255 cm −1 with C 6D 6). The only one significant difference lies on the positions of the carbon-metal vibrations respectively at 290 and 360 cm −1 on the Ni(111) and (100) faces. These results provide evidence that the configuration of the adsorbed species are the same on the two surfaces. An associative adsorption, with chemisorbed benzene molecules π bonded to the metallic substrate and with their rings parallel to the surface, is proposed. Alternative interpretations of the vibrational spectra are given according to the so called “surface selection rule”, which implies that only totally symmetric modes are ELS active, or in terms of the most infrared active modes of the gaseous benzene.