The process of whole molecule libration, or torsional oscillation, of molecular dipoles evolves dynamically in supercooled solutions and glasses on an observable time scale extending from picoseconds to kiloseconds and longer. This can be measured using the dielectric loss spectrum of rigid dipolar solute molecules dissolved in glass‐forming solvents such as decalin. The complete spectrum extends from below 100 Hz to THz frequencies, where the short time behavior can be detailed using the far infrared power absorption coefficient. This occurs universally and is characterized here for the first time as the γ process—the high frequency adjunct of the α and β processes discovered by Johari and co‐workers. Results are presented over a broad frequency range (kHz to the far infrared, discontinuous) for the halogenated benzenes and for methylene chloride. In C6H5F/decalin there is a well defined β process, in C6H5Cl/decalin it is much less intense, and in C6H5Br/decalin it is either unresolved or vanishingly small. The multidecade loss profile of methylene chloride is reported in various glass‐forming solvents. The loss shows three peaks (α, β, γ) in a total range of over 12 decades. Both the α and β processes in various glasses and supercooled solutions are associated with very high activation energies of about 100 kJ/mol. This feature appears to be specific to CH2Cl2. The high frequency (γ) part of the loss in the far infrared region may be studied in detail because of the relation between the dielectric loss and the optical power absortion coefficient. In some solvents there is a very large difference between the γ profile in the liquid at ambient temperature and the low temperature glass.
Dielectric and far infrared study of solutions in the glassy state from 100 Hz to 10 THz: Discovery and characterization of the universal γ process
C. J. Reid, M. W. Evans; Dielectric and far infrared study of solutions in the glassy state from 100 Hz to 10 THz: Discovery and characterization of the universal γ process. J. Chem. Phys. 1 March 1982; 76 (5): 2576–2584. https://doi.org/10.1063/1.443235
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