Raman spectra from ethylene and deuterated ethylene chemisorbed on a silica-supported nickel catalyst

Abstract

The Raman spectra of ethylene and deuterated ethylene chemisorbed on silica-supported nickel have been measured in the frequency range 50–3400 cm −1. At room temperature, a Raman spectrum is observed which corresponds to ethylene chemisorbed under dehydrogenation and it is rather similar to the spectrum of chemisorbed acetylene. For a comparison therefore, the Raman spectra of acetylene and deuterated acetylene were also measured. In addition, the vibrational spectrum of chemisorbed benzene was recorded. At temperatures T ⩽ 200 K, ethylene is found to be associatively chemisorbed without dehydrogenation. The vibrations observed are described in the approximation of a surface molecule with covalent bonding to two or three surface nickel atoms. The symmetry seems to be slightly distorted C 2v or C s. The vibrational spectrum is discussed with respect to a metal- surface selection rule. In order to improve the reliability of the assignments for localized vibrational modes, a normal coordinate analysis and a force constant calculation have been done for chemisorbed acetylene.