IR-spectroscopy of CO adsorption on mixed-terminated ZnO surfaces

Abstract The adsorption of CO on two different mixed-terminated, single-crystal surfaces of zinc oxide, ZnO(10 1 − 0) and ZnO(11 2 − 0), was investigated by employing infrared reflection absorption spectroscopy (IRRAS) using p- and s-polarized light. For both surfaces, one negative CO band was observed only for p-polarized light, indicating that CO is bound to the surface Zn 2 + sites in a nearly upright geometry. In addition, we observed a substantial coverage-induced frequency shift for CO adsorption on both ZnO surfaces. For ZnO(10 1 − 0), the ν (C-O) band shows a red shift of 16 cm − 1 when increasing the CO coverage from 0.5 ML (2185 cm − 1 ) to 1 ML (2169 cm − 1 ). On the ZnO(11 2 − 0) surface, for isolated CO molecules, a frequency of 2192 cm − 1 was detected. The CO band shifts to 2170 cm − 1 at full monolayer. On both surfaces, the coverage-dependent frequency shift is attributed to a combination of dynamic and substrate-mediated static adsorbate–adsorbate interactions.