Slow Relaxation Processes in SF6 Gas After Pumping by a CO2 Laser Pulse

The vibrational energy relaxation and distribution in SF 6 at the collisional condition of 2 Torr wasmeasured with the pump-probe method by use of two tunable CO 2 300 ns-pulse lasers at the delay time upto 400 μs. The 10.6 μs P(30) pump intensity was 0.4 J/cm 2 . The probed spectra, divided into two parts, theinduced transmission at the P(10)–P(22) and the absorption at the P(24)–P(32), were red-shifted by 50 μsand then slowly back to the initial. The time variation of induced signals was divided into the four regionsdue to the following processes; (I) the formation of nonthermal distribution in the ν 3 mode andquasi-continuum with 1 μs, (II) the broad redistribution by the rise-up of vibrational temperature in50 μs-duration, (III) the molecular diffusion or expansion out of the pumped region locally heated up bythe V–T relaxation in another 60 μs, (IV) the gas cooling corresponding to the energy relaxation orpopulation depletion over 400 μs. So, this pump-probe method at the collisional conditions will easily give us some informations, with a short gas cell and a suitable time scale, on those slow processes.