二溴代烷烃的紫外光解动力学研究  

Ultraviolet Photodissociation Dynamics of Dibromoalkane

作　　者：姬磊[1] 唐颖[1] 朱荣淑[1] 唐碧峰[1] 张嵩[1] 张冰[1] 

机构地区：[1]中国科学院武汉物理与数学研究所波谱与原子分子物理国家重点实验室,武汉430071

出　　处：《化学学报》2004年第13期1211-1216,J002,共7页Acta Chimica Sinica

基　　金：中国科学院创新基金 (No.T0 2 2 2 0 5)资助项目

摘　　要：利用飞行时间质谱装置研究了 2 3 4和 2 67nm激光作用下二溴甲烷、二溴乙烷、二溴丙烷和二溴丁烷分子的光解离过程 .研究表明二溴代烷烃分子在紫外激光的作用下主要是断裂C—Br键解离出一个Br原子 ,并且存在两种可能的布居 :基态Br( 2 P03 / 2 )和激发态Br ( 2 P01/ 2 ) .通过共振增强多光子电离技术探测两种光解产物布居的分支比 .对比得到了分子构型对称性不同的二溴代烷烃的分支比 。The photodissociation dynamics of CH2Br2, C2H4Br2, C3H6Br2 and C4H8Br2 near 234 and 267 nm have been studied using time-of-flight mass spectrometry. It was found that photoexcitation of dibromoalkane in IN absorption band results in prompt fission of the C-Br bond, producing two distinguishable photodissociation products: ground state Br(P-2(3/2)0) and spin-orbit state Br(P-2(1/2)0) To achieve state-selective detection of Br and Br*, a (2 + 1) resonance-enhanced multiphoton ionization (REMPI) scheme was employed. The branching ratio of the photodissociation products was extracted from the relative signal intensities of Br* and Br in the REMPI TOF spectra. The findings of this work reveal that a nonadiabatic curve-crossing between the (3)Q(0) and (1)Q(1), states is responsible for the reduction in the symmetry of the molecule in the photodissociation process To C4H8Br2, the further reduction in the molecular symmetry induces level-splitting to more electronic states, then the coupling between these states causes an avoided crossing, which can change the photodissociation paths accordingly. The wavelength dependence of the branching ratio for both Br and Br* channels provides insight into the nature of the electronic excited states which contribute to the absorption spectrum and the role of nonadiabatic curve crossing in the photodissociation process.

关 键 词：二溴代烷烃 光解动力学 碳-溴键 共振增强多光子电离技术 飞行时间质谱 分支比 臭氧层 

分 类 号：O643.1[理学—物理化学]