Studies on Laser Induced Dispersive Fluorescence Spectroscopy of SO2 Molecule Excited by Two-Photon

The processes of excitation and complicated de-excitation of A-symmetric state in the first-excited band of SO2 molecule were studied experimentally with the techniques of two-photon laser induced dispersive fluorescence spectroscopy where a pulsed dye laser (579 nm) was used as excitation sources. The SO2 molecule which were excited from ground state X(1)A(1) to the high vibrational levels of A(1)A(2) state by absorbing two photons, will realize the repopulation in several vibration-rotational energy levels of A(1)A(2), (BB1)-B-1 and a(3)B(1) states by internal energy conversion and collision relaxation. Because of transitions to the different vibrational levels of ground electronic state X(1)A(1) from the ground vibrational levels of A(1)A(2), (BB1)-B-1, and a(3)B(1), the fluorescence spectrum envelopes centered at 305 and 425 nm and the regular fluorescence lines centered at 347.2 nm were formed in the fluorescence spectra. In addition, the process of tri-photon excitation X(1)A(1)->(CB2)-B-1 of SO2 molecule was observed, and the result of the process was the fluorescence spectrum envelope in 200 similar to 278 nm and the overlapping fluorescence lines centered at 425 nm. The harmonic frequencies of the symmetry stretch vibration and the bendvibration and the anharmonic constants of stretch vibration mode and the bend vibration mode of related states were calculated from the experimental data.