Three different ultrasonic techniques, pulse echo, HRB (highhyphen;resolution Bragg reflection), and Brillouin scattering were used to measure the sound velocity and absorption in 1,2hyphen;dibromoethane at 11, 20, and 30thinsp;deg;C over the frequency range from 3 MHz and 6 GHz. The observed results showed a typical spectrum for a single relaxation process, from which the relaxation frequency and strength were determined. The temperature dependence of the relaxation frequency and strength suggested that the activation energy for thegauchemolecule is 3.0plusmn;0.5 kcal/mol and that the energy difference is 1.3plusmn;0.2 kcal/mol, respectively. The magnitude of the relaxation strength was successfully described by taking the effect of the volume change into account, and Dgr;V/Vwas estimated to be 0.05.
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