TEMPERATURE-DEPENDENT EFFECTS OF SUBSTRATE PHONONS ON THE LINE BROADENING AND FREQUENCY-SHIFT OF AN ADMOLECULE

Vibrational modes localized at an adsorbed molecule are influenced by their anharmonic interactions with delocalized phonons of the substrat e. These interactions include both the adsorption potential between th e molecule and the surface atoms, and the anharmonic couplings among t he substrate atoms themselves at the adsorption site. While the former plays a significant role at bridge sites, for example, the latter is also effective at on-top sites, as shown by model calculations of the temperature-dependent vibrational line width and shift.