Dielectric Dispersion in the Microwave Region of Six Tetrasubstituted Methanes in the Solid State

Abstract

A method is described for the measurement of dielectric constant and loss at microwave frequencies and low temperatures. The dielectric constant and loss at 3.22 cm wavelength (9.32×109 cycles/sec) have been measured over a range of temperature in the solid state and in the liquid near the melting point for t-butyl chloride, t-butyl bromide, 2,2-dichloropropane, methyl chloroform, 2-chloro−2-nitropropane, and 2,2-dinitropropane. 1,1-Dichloro−1-nitropropane also has been measured as a supercooled liquid. The six tetrasubstituted methanes, previously found to show molecular orientational freedom in the solid state for some distance below the melting point, give evidence of very short dielectric relaxation times in this region. The relaxation times increase from a very low value for t-butyl chloride to values such that large dielectric loss is observed near 3 cm for 2-chloro−2-nitropropane and 2,2-dinitropropane. The relaxation times in the solid rotator phases and in the liquid are compared, and the results are discussed in terms of intermolecular forces which give rise to potential energy barriers restricting rotation.