Sound velocity and absorption measurements were made in a number of aqueous electrolytic solutions, principally the 2ndash;2 valent sulfates. Ultrasonic pulse measurements were used in the frequency region 30ndash;900 MHz, and the technique of Brillouin light scattering was employed in a number of measurements between 6000 and 7000 MHz. In several of the solutions studied, the ultrasonic data indicate the existence of two relaxation processes with relaxation times lying in the range 5thinsp;times;thinsp;10minus;9ndash;2thinsp;times;thinsp;10minus;10sec. These two relaxations, considered together with the previously observed long relaxation time process, can be interpreted in terms of the Dieblerndash;Eigen model of ionic association which predicts three relaxation processes. The shortest relaxation time process was identified with the diffusion controlled approach of the hydrated ions. The calculation of the appropriate reaction rate constants using data by other workers below 50 MHz and the present data above 50 MHz was carried out. The results are compared with earlier results based on data taken below 200 MHz.
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