Vibrational relaxation in binary mixtures

Abstract

Ultrasonic and hypersonic studies were made for vibrational relaxations in two systems of liquid mixtures, furan‐cyclohexane and dichloromethane‐benzene. High‐resolution Bragg reflection method and Brillouin scattering were used to measure the velocity and absorption at 20 °C over a frequency range from 100 MHz to 7 GHz. In furan‐cyclohexane mixtures, vibrational relaxation time for furan molecule was determined from velocity dispersion curve and found to decrease strongly with the addition of cyclohexane. This decrease was interpreted in terms of the large efficiency in vibration‐vibration (V‐V) energy transfer between the lowest vibrational mode of furan (605 cm−1 and the nearest mode of cyclohexane (522 cm−1). The rate constant of the V‐V transfer was estimated from the concentration dependence of the relaxation time. Vibrational relaxation time for cyclohexane was found to decrease slightly with the addition of furan. Also in dichloromethane‐benzene mixtures, it appears that V‐V transfer is responsible for the change in the relaxation time.