激光光解NO_2产物——氧原子O(~3P_(J''))的REMPI离子谱

REMPI Spectrum of Atomic Oxygen O(~3P_(J'')) from Photofragment of NO_2

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NO_2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(2 p^3P_J~″=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f_1=I(~3P_1)/I(~3P_2)与fo=I(~3P_0)/I(~3P_2)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~3P_2:~3P_1:~3P_0=1:0.6:0.2).这是由于样品(NO_2)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(~3P_J~″)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(~3P_J~″=2,1,0)是统计分布的.

The ion spectrum of the O(3 PJ') 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 3 PJ'→3p 3 PJ' )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(3 PJ') is ionized by (2 + 1) multiphoton absorption process. The obtained three spin-orbit sublevels branching rations of f1 = I(3 P1) / I(3 P2) and f0 = /(3 P0) / /(3 P2) for O (3 PJ'=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 sub-levels O(3PJ'=2,1,0) is statistical distribution.