Residual absorption of 1,1,1-trichloroethane and some related broad band absorption studies

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Abstract
As a result of dielectric work mainly at 70 and 140 GHz and an extrapolation of the data by the Cole-Cole equation to obtain the permittivity of very high frequencies (ε∞) the residual dispersion (ε∞ − n2) of 1,1,1-trichloroethane would appear to be very small indeed at 293 and 318°K. However, the liquid exhibits strong broad band absorption. It would seem, therefore, that either the Poley concept of residual absorption is inadequate for 1,1,1-trichloroethane or that the data at frequencies significantly greater than 140 GHz do not fit a Cole-Cole plot and the resulting extrapolation yields a misleading value of ε∞. The fairly intense far-infrared absorption of 1,1,1-trichloroethane would support the latter as being the case, especially since the ε∞−nD2 at 253°K is ∼0.3, while the absorption intensities of the broad band appear essentially unaltered over the 227–310°K range. Far-infrared studies have also been carried out on 2,2-dichloropropane over a fairly wide temperature range in the liquid and solid phases, and the results support the concept that the broad band absorption in the liquid phase of polar substances may have a large contribution from molecular rotation (which could be somewhat restricted) since for both 2,2-dichloropropane and 1,1,1-trichloroethane, on their passing from the liquid phase to the adjacent solid phase, the half-band width and αmax values do not change appreciably. On further cooling of these solids below the lambda point, the far-infrared spectrum changes appreciably and characteristic lattice bands result which are to be related to the more rigorous order of a lattice and the lack of molecular rotation. No rotator solid phase has been detected for chloroform, and in this case a considerable change occurs between the broad band absorption of the liquid at room temperature and the lattice bands of the solid.