Abstract

The adsorption of CO on two different mixed-terminated, single-crystal surfaces of zinc oxide, ZnO(1010) and ZnO(1120), was investigated by employing infrared reflection absorption spectroscopy (IRRAS) using p- and spolarized light. For both surfaces, one negative CO band was observed only for p-polarized light, indicating that CO is bound to the surface Zn2+ 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(1010), 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(1120) 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. 

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