紫外波段CH_2I_2分子的光解离动力学研究

UV photodissociation dynamics of CH_2I_2 molecule

利用离子速度成像方法 ,研究CH2 I2 分子在 2 77— 30 5nm范围内若干波长处的光解离动力学 .通过同一束激光经 (2 +1)共振多光子电离 (REMPI)过程探测光解碎片I(2 P3 2 )和I (2 P1 2 ) ,得到了不同激发波长处的离子速度分布图像 ,从而获得CH2 I2 光解产物的能量分配和角分布 .实验发现 ,碎片CH2 I自由基有很高的内能激发 ,约占总可资用能的 80 %,该能量分配可以较好地用冲击模型来解释 .实验还发现 ,产物I(2 P3 2 )和I (2 P1 2 )具有很不相同的平动能分布 ,结合所得到的碎片能量分配和角分布 ,我们对碎片I(2 P3 2 )和I (2 P1 2 )生成机理进行了分析 ,指出CH2 I2分子电子激发态的绝热和非绝热解离决定了碎片的平动能分布 .

Photodissociation dynamics of CH 2I 2 moleculae was investigated at different wavelengths of 277 to 305nm by an ion imaging spectrometer operated under optimal conditions for velocity mapping, where the ions were generated from (2+1) resonance-enhanced ionization (REMPI) of the photofragments I( 2P 3/2) and I *( 2P 1/2) at the same wavelength as that of the photolysis UV laser. The released kinetic energies and the angular distributions of both fragments at different photolysis wavelengths were derived from the three-dimensional velocity images. It was found that the photofragment of CH 2I radical was highly excited. About 80% of the total released energy deposits into internal freedom. This fact can be explained by the impulse model. A remarkable difference between the kinetic energy distributions of I( 2P 3/2) and I *( 2P 1/2) was found. The dissociation mechanism of the formation of both I( 2P 3/2) and I *( 2P 1/2) fragments is discussed in terms of anisotropy parameter and energy partition. The kinetic energy distributions of the I( 2P 3/2) and I *( 2P 1/2) fragments are determined by the adiabatic and nonadiabatic dissociation processes in the electronically excited states of CH 2I 2.