VIBRATIONAL-RELAXATION OF HIGHLY EXCITED SIF4 AND C6F5H BY AR

The vibrational relaxation of SiF4 and C6F 5H in an Ar bath was measured as a function of initial energy using the method of time-resolved optoacoustics. SiF4 was found to relax nonexponentially, with a rate constant which varied approximately as the vibrational energy raised to the 3/2 power. This behavior is similar to that observed earlier for SF6 + Ar below the bottleneck. In contrast, C6F5H was observed to decay exponentially, as expected for a large molecule in the quasicontinuum. These two types of behavior are discussed in the context of previously proposed propensity rules for the vibrational relaxation of highly excited molecules. © 1990 American Institute of Physics.