Vibrational modes of c(4x2) CO-Pt(111) from first-principles calculations

The vibrational modes of CO adsorbed on Pt(111) in the c(4 X 2) structure have been studied within the harmonic approximation, using density functional calculations. The characters, fundamental energies, and dipole activities have been determined for all modes. For top-adsorbed molecules, the static adsorbate-adsorbate interaction is found to induce energy splitting among frustrated lateral translational modes, which have previously been assumed to be degenerate, and a reassignment of previously measured vibrational energies to low-energy modes is proposed. For bridge-adsorbed molecules, the frustrated rotational fundamental transitions, which should be dipole forbidden from the local adsorption site symmetry, are found to be weakly dipole active. (C) 2001 American Institute of Physics.