紫外波段CH2I2分子的光解离动力学研究

利用离子速度成像方法,研究CH2I2分子在277—305nm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(2P32)和I(2P12),得到了不同激发波长处的离子速度分布图像,从而获得CH2I2光解产物的能量分配和角分布.实验发现,碎片CH2I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(2P32)和I(2P12)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(2P32)和I(2P12)生成机理进行了分析,指出CH2I2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. 关键词： CH2I2 离子速度成像 绝热和非绝热解离

UV photodissociation dynamics of CH2I2 molecule

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.