On the Optical Absorption of Thin BaO Film in the Ultraviolet Region

By measuring the optical transmittance of evaporated BaO film in vacuum, it has been found that the threshold for absorption occurs at 3200 Å and the second rapid rise in absorption begins at 2500 Å approximately. Two absorption bands have been observed in the region ranging from 2500 Å to 3200 Å: one has a maximum at 2800 Å and the other has a maximum at about 3000 Å. The latter absorption hand is new and has not been observed so far by the method of optical transmittance, though its presence has been suggested by the photoconduction of BaO single crystal. The influence of oxygen vapour upon the absorption bands has also been investigated, and it has been observed that when thin BaO film was exposed to oxygen, the absorption bands in the region 2500 Å–3200 Å vanished out suddenly and the film became transparent in the region of wavelengths longer than 2500 Å.