The absorption spectra of chlorate, bromate, iodate, and hypobromite ions and of hypobromous acid were measured.The decomposition of bromate ion was investigated in the light of a mercury arc in the spectral region: 1900A to 2600A. The quantum yield of the decomposition is 0.19. The main decomposition reaction leads to the formation of hypobromite and molecular oxygen. The irradiation of hypobromite ions leads to the formation of bromide and bromate ions in a ratio of about 4 to 1 and to the evolution of oxygen. The decomposition of chlorate ion and iodate ion is analogous to that of bromate. It is assumed that in all these cases the primary process of light absorption consists of the transfer of an electron to the hydration layer. In the case of halate ions, the photo‐chemical reaction can be formulated as a decomposition of the complex (XO3−·H2O) to XO−+H2O+O2; in the case of the hypobromite, as the decomposition of (XO−·H2O) to X−+H2O+O. In the latter case the oxygen atoms formed are responsible for the formation of bromate.
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