The optical absorption in the region 20ndash;100 cmminus;1has been measured by Fourier transform spectroscopy for the pure liquids of theorthoandmetaisomers of difluorohyphen;, dichlorohyphen;, and dibromobenzene at a temperature of 20deg;C. The absorptions are very broad having halfhyphen;widths of about 80 cmminus;1and the peak value of the absorption coefficient is higher than that predicted by the Debye theory of dielectric relaxation for all the substances studied. The theories proposed for absorption in the farhyphen;infrared region are inadequate and do not explain the experimental results. It is concluded that the strong absorption is predominantly due to the rotational transitions of the molecule and that a similar phenomenon should occur in all polar liquids.
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