Collisional deactivation of highly vibrationally excited SO2: A time-resolved FTIR emission spectroscopy study

Time-resolved Fourier transform IR emission spectroscopy, capable of 10(-8) s and 0.1 cm(-1) spectral resolution, has been used to study the collision al deactivation of highly vibrationally excited SO2 by bath-gas molecules A r, N-2, O-2, CO2 and SF6. The vibrationally excited SO2 were initially prep ared with 32,500 cm(-1) energy in the (X) over tilde (1)A(1) state by the p ulsed 308 nm laser excitation followed by internal conversion. The entire c ollisional deactivation process of the excited SO2 was monitored by time-re solved IR emission spectra through the IR active transitions. The average e nergy, (E), of excited SO2 was extracted from the IR emission bands using k nown vibrational constants and selection rules. (E) is further used to deri ve the average energy loss per collision, (DeltaE), by each of the bath-gas molecules. The results show that (DeltaE) increases from mono- and diatomi c quenchers to more complex polyatomic molecules, as V-V energy transfer co ntributes to V-T/R. For all bath molecules, (DeltaE) increases with (E) and displays a marked increase at (E) approximate to 20,000 cm(-1). The observ ed threshold behavior most likely arises from intramolecular vibronic coupl ing within SO2 and implies the importance of long range interaction in inte rmolecular energy transfer.