Photodissociation dynamics of free radicals

自由基的光化学反应在大气和星际化学反应中起着重要的作用。用二维离子成像方法研究了C_nH_m的离解动力学。在光激发下进入（pi, pi<@D1**@>D1）状态的氯乙烯解离成乙烯基自由基和氯原子。平动能量分布由两部分组成；一个是高各向异性的类高斯平动能量分布，beta=1.0(]SY.+- .[)0.2；另一个是低各向异性的统计分布，beta=0.3 （]SY.+-）。(0.2)。低平动能组分的解离速率常数估计为10<@D111@>D1- 10<@D112@>D1 s<@D1-1@>D1。紫外光解二氯乙烯时，在氯原子和乙炔之后存在C_2H_2Cl自由基的二次解离。在193nm光激发下，约100%的C_2H_2Cl自由基发生二次解离。

Photochemical reaction of free radicals plays an important role in the atmospheric and interstellar chemical reactions. The dissociation dynamics of C_nH_m have been studied by using two dimensional ion imaging method.In the photoexcitation into (pi, pi<@D1**@>D1) state of vinylchloride dissociates into vinyl radical and chlorine atom. The translational energy distribution consists of two components ; one is a Gaussian-like translational energy distribution with high anisotropy, beta=1.0(]SY.+-。[)0.2, while the other is a statistical distribution with low anisotropy, beta=0.3 (]SY.+-。[) 0.2. The dissociation rate constants for the low translational energy component is estimated to be 10<@D111@>D1- 10<@D112@>D1 s<@D1-1@>D1.In the case of ultraviolet photodissociation of dichloroethylenes, there exists secondary dissociation of C_2H_2Cl radical following to chlorine atom and acetylene. At 193 nm photoexcitation, about 100% of C_2H_2Cl radical undergo to the secondary dissociation.