The structure of benzene chemisorbed on raney nickel; a neutron inelastic spectroscopy determination

Abstract

Abstract The vibrational spectrum of benzene chemisorbed on Raney nickel was determined by neutron inelastic spectroscopy (INS). The valence force field of the model molecule CrC 6 H 6 (CO) 3 was transferred to chemisorbed benzene by changing only a few force constants. The frequencies calculated with this new force field agree with the published ELS spectra from these systems. We thus propose a new and consistent explanation of the ELS spectra. We obtain good agreement between calculated and experimental INS spectra if we add to the calculated spectrum the contribution from chemisorbed hydrogen, corresponding to the 10% of the hydrocarbon molecules which have lost their hydrogen. The strong perturbation of the adsorbed molecule results in a 20% weakening of the CC stretching force constant and of the (CC) interaction constant. The bonding of the molecule to the Raney nickel surface is stronger than on Ni(111) or Ni(100). Finally the benzene lies flat on the metal surface and is preferentially bound to one nickel atom, at a distance of 2.5 ± 0.5 A.