Microwave and Infrared Dielectric Relaxation of Alkylcarbonates, Chloroform and Their Mixtures at 25 deg C

Microwave data yielding the complex permittivity e*=e'=Je'', infrared and visible refractive indices, and infrared attenuation coefficients for liquid dimethyl-carbonate ( (CH30) 2CO; abbrev: DMC), chloroform, and their mixtures have been recorded at 25 deg C. For pure DMC the real part of the complex permittivity e' versus frequency shows two relaxation domains: the microwave frequency range interpreted as the rotational relaxation of the methoxy groups, -OCH3, around the carbonyl moiety, C=O, and a newly discovered relaxation domain at infrared frequencies. The profile of n2IR, (the squared refractive index) versus frequency for pure CHCl3 reveals a new dielectric phenomenon hinted at by literature data obtained at far-IR frequencies. Mixtures of DMC and CHCl3 have a microwave dielectric spectrum that differs markedly from that which would be expected for mole fraction XDMC=0.50, if the two components did not interact strongly with each other. The dielectric relaxation frequencies of pure DMC and pure CHCl3 are fr=22 GHz and 27 GHz respectively. When mixed at a composition XDMC=0.50, a dielectric relaxation spectrum is produced that can be interpreted by a Cole-Cole distribution with an average relaxation frequency fr = 17 GHz and a distribution relaxation parameter a=0.08 (O<a<l with a=O for a singe Debye relaxation process). This dielectric relaxation is ascribed to the formation of H-bonded complexes arising form interactions of the proton of CHCl3 and the carbonyl moiety of DMC.