Collective vibrational modes in isotopic mixtures of CO adsorbed on Cu (100)

Isotopic mixtures of CO adsorbed on Cu(100) have been studied by infrared spectroscopy. For mixtures of ¹²C ¹⁶O/ ¹²C ¹⁸O at a constant coverage of 0.5 it was found that the molecules constitute a collective vibrational system. The C-O stretching vibrations were studied as a function of composition of the overlayer and the data are successfully interpreted by a dipole — dipole coupling theory.