Line shape of the stretching vibration of CO adsorbed on rough copper surfaces

The asymmetric broadening of the stretching vibration in surface enhanced Raman scattering of CO adsorbed on cryocondensed copper films can be explained by considering dipole–dipole interaction of the molecules and elastic scattering at structures of atomic roughness. Calculated line shapes are in good agreement with the experiment, including the low wavenumber shoulder. The variation of the line shape with the CO exposure can be modelled by an increased vibronic polarizability which is consistent with the increase of the dynamical dipole moment for the chemisorbed molecule due to back donation into the CO 2π* orbital.