Vibrational and Rotational Relaxation in Sulfur Dioxide

Abstract

Ultrasonic absorption measurements have been used to study the vibrational and rotational relaxation in SO2 from 290 to 1090°K. This work extends the temperature range of earlier investigations by 500°K and is in agreement with the other studies in the low-temperature region. The vibrational data has been analyzed by assuming that the 518-cm−1 node exhibits a relaxation time τ1, that the 1151- and the 1361-cm−1 modes relax together with a relaxation time τ2,3, and that the two relaxations occur in parallel. It is found that τ1 increases with increasing temperature, while τ2,3 decreases with increasing temperature in the normal manner. The two vibrational collision numbers are a factor of 10 apart at room temperature but approach each other at high temperature. This is the first ultrasonic measurement of rotational relaxation in SO2, and the results confirm those of a previous thermal transpiration measurement but conflict with an earlier thermal conductivity measurement.