Infrared study of oxygen adsorption on impure zinc oxide

Absorption bands are observed in the 2200-1700 cm⁻¹ region when strongly electronegative gases such as oxygen and chlorine are adsorbed on zinc oxide powder. These bands are related to carbon and nitrogen present as impurities in the zinc oxide. Efforts have been made to determine whether the bands correspond to stretching vibrations or whether they are due to electronic transitions from impurity donors to discrete levels lying 0·2–0·3 eV above the impurity levels. Use of carbon-13 as an impurity has identified a strong band at 1990cm⁻¹ as a carbon-oxygen stretching vibration. It is presumed that other observed bands are also of vibrational rather than electronic origin. A suggested mechanism implies that adsorption of electron withdrawing gases brings about formation of bonds between impurity atoms and oxygen within the bulk of the zinc oxide. This phenomenon appears to be limited to a depletion layer 10–30 Å in depth.