On the Infrared Spectra of Fluoro-, Chloro-, Bromo- and Iodobenzene in the Vapour State

The infrared speutra of fluorobenzene, ehlorobenzene, bromobenzone and iodobenzone in the vapour state have been studied using a Perkin-Elmer one metre gas cell and Model 21 spectrophotometer and compared with the spectra of the pure liquids and of their solutions in carbon tetrachloride and chloroform. Significant changes are observed with the change of state. From the spectra of fluorobenzene and chlorobenzene in the different states it has been concluded that in both these cases the vapour consists of both monomeric and dimeric molecules and the liquid consists almost wholly of dimers. In the other two cases the vapour consists predominantly of monomeric molecules and in the liquid state there is a smaller percentage of monomeric molecules and a greater proportion of dimeric molecules. From a comparison of the spectra with the Raman spectra, some of the bands not assigned by previous workers have been assigned to relevant models of vibration of the molecules