Low Temperature Vibrational Relaxation of Gaseous CF₃Cl, CF₃Br, CHF₂Cl, and CH₃Cl

Abstract

Ultrasonic absorption measurements are reported for gaseous CF3Cl, CF3Br, CHF2Cl, and CH3Cl between room temperature and the lower temperatures 163 K, 193 K, 198 K, and 213 K, respectively. Starting from a statistical point of view, the relaxation behavior is divided into three classes, which are associated with the positive, zero, and negative slope in a log(k) versus 1/T plot. On this basis the vibrational relaxation behavior of CF4, CF3Cl, CF3Br, CHF3, CHF2Cl, CH3Cl, NF3, PF3, and BF3 is discussed especially in the critical temperature to boiling point region. This temperature region is used as a reference for comparing different molecules.