Zusammenfassung
Dielec. relaxation was measured in liq. formamide (FA), N-methylformamide (NMF), DMF, and N,N-dimethylacetamide (DMA) 238.15-338.15 K in the frequency range from 0.2 to 89 GHz. Whereas the FA spectra can be formally fitted with a Davidson-Cole relaxation-time distribution, two relaxation process can be resolved for the other liqs. For DMF and DMA, the long relaxation time, τ1(T), follows the ...
Zusammenfassung
Dielec. relaxation was measured in liq. formamide (FA), N-methylformamide (NMF), DMF, and N,N-dimethylacetamide (DMA) 238.15-338.15 K in the frequency range from 0.2 to 89 GHz. Whereas the FA spectra can be formally fitted with a Davidson-Cole relaxation-time distribution, two relaxation process can be resolved for the other liqs. For DMF and DMA, the long relaxation time, τ1(T), follows the Vogel-Flucher-Tammann equation. For these liqs., τ1(T) probes the essentially isotropic rotational diffusion of the mol. dipole vector. For the hydrogen-bonding liqs. FA and NMF, a modified Eyring equation is more appropriate to describe τ1(T). From the parameters the av. no. of monomers in the chains of H-bonded NMF mols. is deduced, as well as the no. of hydrogen bonds which must be broken before relaxation in FA can occur. The data suggest that the obsd. high-frequency contribution in the spectra mainly reflects the onset of internal contributions.
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