Vibrational excitations and structure of CO chemisorbed on Cu(100)

Abstract

The local adsorption site for CO chemisorbed on Cu(100) at 80 K has been investigated by vibrational spectroscopy at different structural situations as defined by low-energy electron diffraction. The high-resolution electron energy loss spectrum for the c(2 × 2) CO structure (coverage 0.5) is compatible with a terminal CuCO bond. The spectrum shows two vibrational loss lines at 43 and 260 meV due to excitations of the CuC and CO stretcning vibrations respectively. The CO stretchning vibration is excited via dipole interaction for primary electron energies 1–4 eV. An effective dynamic charge of 0.64 e is deduced in good agreement with infrared reflection-absorption data. The preceeding CO lattice gas is also characterized by the terminal bond configuration. The spectrum for the CO compression structure at coverage 0.57 is tentatively interpreted in terms of an alternative site (terminal and bridge) absorption model proposed by Pritchard. A brief comparision with the Ni(100)-CO system is made.