Bending vibrations of OH groups resulting from H2 dissociation on ZnO

Abstract

Dissociative adsorption of H₂ on ZnO, apart from the bands due to OH and ZnH stretching vibrations, gives rise to bands at ca. 840 and 810 cm^–1 which can be attributed to the bending modes of these surface structures. Analysis of the integrated intensities of the bands arising after H₂ and HD adsorption at 100 and 300 K shows that both the 840 and 810 cm^–1 bands are due to ZnOH group vibrations. Their shift after ¹⁸O isotope substitution of surface oxygen, only 1 and 2 cm^–1, respectively, implies that they cannot be associated with the Zn—O vibration or its overtone enhanced by Fermi resonance. They should be attributed to two bending modes of surface hydroxyls. After HD and D₂ adsorption a band for the OD bending vibration was detected at 637 cm^–1. In accordance with these data, ν_OH(D)+δ_OH(D) combinations were observed at 4297 and 3195 cm^–1, which give the values of 807 and 611 cm^–1 for δ_OH and δ_OD, corresponding, apparently, to the more intense low-frequency component.