Reduced stretch vibration frequency for CO on Na covered Cu(100)

When Na is coadsorbed with CO on Cu(100), EELS show a peak at around 0.17 eV loss energy in addition to the peak at 0.26 eV which is characteristic of CO on Na-free Cu(100). The low energy peak is ascribed to CO molecules adsorbed near Na atoms. The appearance of both the shifted and unshifted loss peaks demonstrates the local nature of the alkali-CO interaction for the present system.