Zusammenfassung
The results of dielec. relaxation expts. on benzonitrile, propylene carbonate and butylene carbonate, performed between 228.15 K and 338.15 K in the frequency range 0.1 ≤ ν/GHz ≤ 89 are presented. The spectra of the three liqs. can be formally fitted with two relaxation processes. The long relaxation time, τ1(T), is equally well described by the Vogel-Fulcher-Tammann and the mode-coupling ...
Zusammenfassung
The results of dielec. relaxation expts. on benzonitrile, propylene carbonate and butylene carbonate, performed between 228.15 K and 338.15 K in the frequency range 0.1 ≤ ν/GHz ≤ 89 are presented. The spectra of the three liqs. can be formally fitted with two relaxation processes. The long relaxation time, τ1(T), is equally well described by the Vogel-Fulcher-Tammann and the mode-coupling theory. However, the parameters differ from literature data for propylene carbonate based on the frequency of max. dielec. loss. This low-frequency dispersion step is attributed to the essentially isotropic rotational diffusion of the mol. dipole vector with the carbonates exhibiting some inter-mol. assocn. For butylene carbonate the fast relaxation process, τ2 ≈ 2 ps, partly arises from the rotation of the Et side chain. However, for all three liqs. the obsd. high-frequency contribution in the spectra reflects the transition from mol. dynamics governed by free rotation to long-time rotational diffusion.
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