Vibronic levels of the 'A2 state of SO2 were excited by crossing a supersonic jet of SO2 with laser radiation corresponding to cold bands in the 3045-3005 A region, and the emission spectrum was detected under different laser-jet geometrical alignments. When the exciting laser beam was allowed to cross the jet just outside the spectrometer's field of view, a vibrational fluorescence spectrum of simultaneously excited low 'A2 levels was measured and was found to be independent of the exciting wavelength. This indicated that these levels were populated through inelastic collisions within the jet and that the low-lying 'A2 levels do in general fluoresce back to the ground state. Fourteen band origins near the 'A2(0,0,0)' -'A1(0,0,0)" transition at 3581 A were thus identified to within f l A . An excitation spectrum recorded while monitoring the fluorescence of these collision-populated low 'A2 levels showed many cold bands that have not been detected before and also showed that the efficiency of energy transfer due to collisions depended on the initially excited vibronic level.

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Spectral characterization of four crude oils was attempted by using a different approach for time-resolved laser-induced fluorescence (TRF) techniques. The TRF spectra were excited by pulsed UV laser radiation at 250 nm and were measured at specific time windows of equal gate widths along the trailing edge of the pulsed laser. Contour diagrams of equal fluorescence intensities were then constructed to serve as unique fingerprints for the crude oils. The method does not require that the laser pulse be deconvoluted from the fluorescence signal, which makes it attractive for remote characterization of crude oil.