激光光解NO2产物——氧原子O(3PJ″)的REMPI离子谱

由Nd:YAG激光器三倍频, 输出波长为λ=355 nm（28 169 cm－1）的激光光解NO2分子产生的氧原子, 通过共振增强多光子电离（REMPI, resonance enhanced multiphoto ionization）及飞行时间（TOF, time of flight）质谱技术, 获得了自旋-轨道精细能级分辨的氧原子O(2p 3PJ″=2, 1, 0)离子谱.氧离子信号强度与UV电离激光能量（λ≈226 nm）之间的关系能用三次方曲线很好拟合, 它表明光解产物氧原子是通过（2＋1）多光子吸收过程而被电离的.由离子信号得到的氧原子基态三个自旋-轨道支能级布居比f1=I(3P1)/I(3P2)与f0=I(3P0)/I(3P2)分别为0.54±0.09和0.20±0.04, 并且在不同的光解激光能量下其布居比保持不变.这一比值与统计分布计算的值为0.6和0.2一致（即统计分布3P2∶3P1∶3P0=1:0.6:0.2）.这是由于样品(NO2)在较低的压力下（1.33×10－4 Pa）和极短的光解-电离时间范围内（10－8 s）, 产物O（3PJ″）支能级间几乎不可能发生碰撞能量转移, 因此, 氧原子三个自旋-轨道角动量分裂能级布居O（3PJ″=2, 1, 0）是统计分布的.

REMPI Spectrum of Atomic Oxygen O(3PJ″) from Photofragment of NO2

The ion spectrum of the O(3PJ″) from the photodissociation of NO2 at laser wavelength λ=355 nm (28 169 cm－1) has been investigated using resonance enhanced multiphoton ionization (REMPI) and time of light (TOF) mass spectrometer technique. The spin-orbit fine structure resolved ion spectrum of the atomic oxygen from the two-photon transition of O (2p 3PJ″→3p 3PJ’)is obtained. The ion signal intensity of oxygen as a function of the UV ionization laser energy (λ=226 nm) can be well simulated with cubic proportional curve. It shows, atomic oxygen O(3PJ″) is ionized by (2＋1) multiphoton absorption process. The obtained three spin-orbit sublevels branching rations of f1=I(3P1)/I(3P2) and f0=I(3P0)/I(3P2) for O(3PJ″=2, 1, 0) are 0.54±0.09 and 0.20±0.04 respectively which is in good agreement with the statistical distribution of 3P2∶3P1∶3P0=1∶0.6∶0.2 .In lower sample(NO2) pressure the collision-induced energy transfer between atomic oxygen sublevels O(3PJ″=2, 1, 0) can’t occur during photodissociation-ionization time (10－8 s).The population of spin-orbit angular momentum split sublevels O(3PJ″=2, 1, 0) is statistical distribution.