Nonresonant Absorption in Symmetric-Top Gases: Dependence of Relaxation Frequency on Temperature

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Abstract
The nonresonant absorption spectra of CHF3, CH3F, and CClF3 were obtained in the gaseous state at various temperatures in the range 230° to 360°K. In all cases the maximum value of the dielectric loss per unit pressure varies as T—2, in accordance with the Debye equation. The variation of relaxation frequency (line width) with pressure and temperature is represented by Δν∞pT—m, where m has the following values: 1.59±0.03 for CHF3, 1.60±0.02 for CH3F, and 1.27±0.02 for CClF3, Since CHF3 and CH3F have rather large dipole moments, the predominant interaction should be of the first-order dipole-dipole type. On this basis Anderson's theory predicts m = 1. Closer agreement with the experimental data is obtained with an expression derived essentially from dimensional considerations of a torque-impulse model, which gives m = 1.5. In the case of CClF3, which has a comparatively small dipole moment, the data indicate that molecular reorientation is governed primarily by forces of shorter range.