ArF laser flash photolysis of hexafluorobenzene vapor: Formation of hot molecules and their collisional relaxation

Time-resolved absorption spectra of hexafluorobenzene vapor have been observed in the time range of 0–2 μs after pulsed ArF laser (193 nm) excitation. The absorption spectrum observed at the time t=0 is attributed to HFB* (S0) (hot hexafluorobenzene with an internal energy of 639 kJ/mol). This transient absorption spectrum can be simulated as a part of the spectrum of the S3(1E1u)←S0 transition at 3050 K on the basis of a modified Sulzer–Wieland model. The collisional deactivation of HFB* molecules is explained in terms of an energy transfer model which assumes that the energy removed per collision depends upon the internal energy.