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

The vibrational energy relaxation and distribution in SF6 at the collisional condition of 2 Torr was measured with the pump-probe method by use of two tunable CO2 300 ns-pulse lasers at the delay time up to 400 μs. The 10.6 μs P(30) pump intensity was 0.4 J/cm2. The probed spectra, divided into two parts, the induced transmission at the P(10)–P(22) and the absorption at the P(24)–P(32), were red-shifted by 50 μs and then slowly back to the initial. The time variation of induced signals was divided into the four regions due to the following processes; (I) the formation of nonthermal distribution in the ν3 mode and quasi-continuum with 1 μs, (II) the broad redistribution by the rise-up of vibrational temperature in 50 μs-duration, (III) the molecular diffusion or expansion out of the pumped region locally heated up by the V–T relaxation in another 60 μs, (IV) the gas cooling corresponding to the energy relaxation or population 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.