The vibrational relaxation of highly excited SF6 by Ar

The method of time-resolved optoacoustics was used to measure the time constant τ for the vibrational relaxation of SF6 by Ar as a function of the average initial excitation 〈〈E〉〉0. It was found that pτ=210±30 μs Torr for 〈〈E〉〉0 between 4000 and 19 000 cm−1, implying nearly pure exponential decay. The average amount of energy change per collision varies linearly with 〈〈E〉〉, having a value of −8 cm−1/collision at 19 000 cm−1. Below 4000 cm−1 pτ increases, approaching the low energy value obtained from IR fluorescence measurements.