Vibrational energy-transfer processes in the CO/Cu(100) system

Dipole-dipole coupling in the (CO)-C-12/Cu(100) system results in a nu(CO) frequency at 2086 cm(-1), which is a shift of +43 cm(-1). The chemical effect (measured here as the difference between the frequency of the singleton at low coverage minus the singleton at high coverage), was found to be -32 cm(-1). Dilution of (CO)-C-12 with Ar at 23 K revealed that at high concentrations, argon underwent island growth. At lower dilutions, two different interactions shifted the observed nu(CO) frequency; charge transfer between Ar and the surface combined with an additional dipole-dipole coupling contribution caused by the dipole induced in Ar by the CO gave a maximum shift of -10 cm(-1) to 2066 cm(-1) at 0.25 ML CO coverage. The temperature dependence of the FWHM and peak position is observed for the compressed (7 root 2 x root 2)R45 degrees structure in the temperature range 23-120 K. No significant temperature dependence of dipole-dipole coupling was observed over this temperature range. The FWHM temperature dependence is conclusively assigned to anharmonic coupling of the CO stretch with the frustrated translation. The total lifetime at 0 K of the nu(CO) mode is determined to be similar to 2 ps.