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

Dipole dipole coupling in the exp 12 CO/Cu(100) system results in a nu sub CO frequency at 2086 cm exp -1 , which is a shift of +43 cm exp -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 exp -1 . Dilution of exp 12 CO with Ar at 23K revealed that at high concentrations, argon underwent island growth. At lower dilutions, two different interactions shifted the observed v sub 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 exp -1 to 2066 cm exp -1 at 0.25 ML CO coverage. The temperature dependence of the FWHM and peak position is observed for the compressed (7root 2 x root 2)R45 deg structure in the temperature range 23-120K. 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 0K of the v sub CO mode is determined to be approx2 ps.