双光子激发SO_2气体激光诱导色散荧光光谱研究

Studies on Laser Induced Dispersive Fluorescence Spectroscopy of SO_2 Molecule Excited by Two-Photon

以脉冲染料激光器579nm激光为激发源,采用双光子激光诱导色散荧光光谱方法,对SO2分子第一激发带A对称电子态的激发及复杂退激发过程进行了实验研究。基态SO2分子吸收两个579nm光子被激发至A1 A2态,通过能量内转换或碰撞弛豫实现在A1 A2,B1 B1与a3 B1态多个振转能级的再布居。三个电子态基振动能级向基态X1 A1不同振动能级跃迁形成了305和425nm处荧光包络与以347nm为中心的规则序列。另外,还观测到了SO2分子的三光子激发过程X1 A1→C1 B2,此激发产生了200～278nm处的荧光包络和425nm处的谱线叠加现象。由实验数据计算出了SO2分子有关电子态的对称振动和弯曲振动模式的基振动角频率及非谐性常数。

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^1A1 to the high vibrational levels of A^1A^2 state by absorbing two photons,will realize the repopulation in several vibration-rotational energy levels of A^1A^2,B1B1 and a^3B1 states by internal energy conversion and collision relaxation.Because of transitions to the different vibrational levels of ground electronic state X^1A1 from the ground vibrational levels of A^1A^2,B1B1 and a^3B1,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^1A1→C1B2 of SO2 molecule was observed,and the result of the process was the fluorescence spectrum envelope in 200-278 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.