SO₂ Laser Excited And Relaxation Process Of The First-excited Band

The electronic states and its features of collision relaxation in the first-excited band of SO2 molecule of the air pollutant have been studied with the techniques of various high sensitivity laser spectroscopy. In which the doubling-frequency and quadruple-frequency outputs of a pulsed Nd:YAG laser and Dye laser pumped by the second harmonic generation of the ns former are used as excitation sources.It's the frist time that the laser induced dispersive fluorescence(LIDF) spectra technique combined with the time tomographic scanning has been used to study the complicated de-excitation process of the first-excited band of SO2 molecule's particles, including fluorescence radiation and collision relaxation, using gated enhanced optical multi-channel spectrum analyzer (OMA) system. The results showed that the SO2 molecules which were excited from ground state X1A1 to the high vibrational levels of B1B1 states by absorbing one photon, radiated the fluorescence and gone to the lower states (the lower excited states or the lower vibrational levels in the first-excited band of SO2) through the progress of collision relaxation at the same time within its lifetime. When the particles gone to some vibrational levels of the excited states through the progress of collision relaxation, it showed that particles were assemble in a short time. The assemble particles of SO2 translated to the different vibrational levels of the ground electronic state, which were showed the fluorescence spectrum envelopes and the regular fluorescence lines in the dispersive fluorescence spectra. It was set the sensitive fluorescence detection wavelength being 425nm in conclusion. There were not only the one photon-excited B symmetric state but also the double photons-excited A symmetric state in the first-excited band. The laser induced dispersive fluorescence(LIDF) spectra technique has been used to study the first-excited band of SO2 molecule's A symmetric state including double photons exciting, fluorescence radiation and collision relaxation, using 532nm laser and 579nm laser as excitation sources respectively. The results was showed as the same as the one photon-excited conclusion. Based on the above study, It has been used to study the fluorescence excited spectra by one photon-excited and double photons-excited in the first-excited band of SO2 molecule, using dye laser as excitation sources in the wavelength of 570nm～605nm and its opposite double frequency range of wavelength. The harmonic frequencies of the symmetry stretch vibration (1=1095.4cm-1), the bend vibration (2=480.0cm-1) and the antisymmetry stretch vibration (3=1160.2cm-1) of A1A1 state were also calculated from the experimental data.