Dynamics of Benzonitrile, Propylene
Carbonate and Butylene Carbonate: the Influence of Molecular Shape and
Flexibility on the Dielectric Relaxation Behaviour of Dipolar Aprotic Liquids
J. Barthel*, R. Buchner, C. Hölzl and M. Münsterer
Z. Phys. Chem. 214, 9, 1213-1231 (2000)
Abstract
The results of dielectric relaxation experiments on benzonitrile, propylene
carbonate and butylene carbonate, performed between 228.15 K and 338.15 K in
the frequency range 0.1 <=n/GHz <=89 are
presented. The spectra of the three liquids can be formally fitted with two
relaxation processes. The long relaxation time, t1(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
maximum dielectric loss. This low-frequency dispersion step is attributed to
the essentially isotropic rotational diffusion of the molecular dipole vector
with the carbonates exhibiting some inter-molecular association. For butylene
carbonate the fast relaxation process, t2
about 2 ps, partly arises from the rotation of the ethyl side chain. However,
for all three liquids the observed high-frequency contribution in the spectra
reflects the transition from molecular dynamics governed by free rotation to
long-time rotational diffusion.
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| (c) 2001 Josef Duschl |
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