离子速度成像系统校准及1,4-氯溴丁烷的紫外光解动力学

大气臭氧层破坏越来越严重, 卤代烷烃在太阳紫外线辐射下解离生成破坏臭氧的游离态卤素原子, 是主要元凶之一. 本文选用碘甲烷作为校准分子, 利用离子速度成像技术和共振增强多光子电离技术测得碘甲烷在266 nm紫外光解离下产生的基态碘原子I(²P_3/2)在不同聚焦电压下的离子速度影像, 得到离子速度成像系统的放大系数N=1.13. 并利用该系统研究了1, 4-氯溴丁烷在～ 234 nm紫外辐射下的解离动力学, 分析讨论了解离产生的基态Br (²P_3/2)和激发态Br^* (²P_1/2)的速度和角度分布信息, 揭示了1, 4-氯溴丁烷在～ 234 nm紫外光解离产生基态Br原子和激发态Br^* 原子的通道都是源于C-Br键排斥势能面上的快速解离. 文中通过计算碎片影像角度分布的各项异性参数β值, 得到了生成基态Br(²P_3/2)和激发态Br^* (²P_1/2) 两个解离通道中的平行跃迁和垂直跃迁比例. 另外, 本文还对氯溴甲烷, 1, 2-氯溴乙烷, 1, 3-氯溴丙烷和1, 4-氯溴丁烷在～ 234 nm下的光解动力学进行比较, 分析得到双卤代烷烃分子解离机理对烷基支链长度的依赖关系.

Calibration of velocity map imaging system and photodissociation dynamics of 1, 4-C4H8BrCl

Depletion of atmospheric ozone layers is more and more serious. Alkyl halides dissociate under the solar UV radiation with the product of free halogen atoms, which greatly damages the ozone layer and is the main culprit for the depletion of ozone layers. In this paper, methyl iodide is chosen as a calibration system of velocity map imaging. Velocity map images of iodine atom I (²P_3/2) at different focus voltages are obtained in the dissociation of methyl iodine under an UV radiation of ～ 266 nm by techniques of velocity map imaging and REMPI (Resonance Enhanced Multiphoton Ionization). The magnification factor N of velocity map imaging system is measured to be 1.13. Photodissociation dynamics of 1, 4-C₄H₈BrCl under an UV radiation of ～ 234 nm is investigated on this velocity map imaging system. The speed and angular distributions of the fragments Br(²P_3/2) and Br^* (²P_1/2) atoms in the dissociation are obtained and analyzed. Experimental results suggest that the dissociation of 1, 4-C₄H₈BrCl to both Br(²P_3/2) and Br^* (²P_1/2) atoms under an UV radiation of ～ 234 nm happens promptly along the C-Br bond via repulsive surfaces after excitation. The anisotropy coefficient β values are obtained from angular distributions of imaging of the fragments Br (²P_3/2) and Br^* (²P_1/2) atoms, by which the ratio between perpendicular transition and parallel transition for those two dissociation channels are calculated. In addition, photodissociation mechanisms of CH₂BrCl, 1, 2-C₂H₄BrCl, 1, 3-C₃H₆BrCl and 1, 4-C₄H₈BrCl at an UV radiation of ～ 234 nm are compared, and the dependences of dissociation mechanisms of dihalogen alkyl compounds on size of the alkyl radical are obtained.