SITE-SPECIFIC, COUPLED-HARMONIC-OSCILLATOR MODEL OF CARBON-MONOXIDE ADSORBED ON EXTENDED, SINGLE-CRYSTAL SURFACES AND ON SMALL CRYSTALS OF PLATINUM

A model describes the vibration of CO molecules adsorbed on extended crystal Surfaces and small particles of platinum by treating the molecules as coupled harmonic oscillators. The frequency of vibration of a single, adsorbed CO molecule and the forces coupling the vibrations of adsorbed CO molecules depend on the coordination numbers of the platinum atoms on which the CO molecules are adsorbed. The model is applied to CO adsorbed on several extended, single-crystal surfaces of platinum and to CO adsorbed on small nearly spherical particles of platinum. A calculation gives the normal modes and infrared intensities for the idealized case of a ring of molecules adsorbed in a great circle about a small particle. This idealized example helps us understand which of the collective vibration modes contribute to the infrared adsorption spectrum for systems with three-dimensional geometries (non-infinite, non-flat surfaces).