2-溴噻吩和3-溴噻吩在267nm的C-Br键解离机理  

C—Br Bond Dissociation Mechanisms of 2-Bromothiophene and 3-Bromothiophene at 267 nm

作　　者：张锋[1,2] 曹振洲[1,2] 覃晓[1,2] 刘玉柱[1,2] 王艳梅[1,2] 张冰[1,2] 

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 [2]中国科学院研究生院,北京100049

出　　处：《物理化学学报》2008年第8期1335-1341,共7页Acta Physico-Chimica Sinica

基　　金：国家自然科学基金(10534010,20673140)资助项目

摘　　要：利用离子速度影像技术,研究了2-溴噻吩和3-溴噻吩两种同分异构体在267nm激光作用下的C—Br键解离机理,获得了光解产物Br(2P3/2)和Br*(2P1/2)的能量和角度分布,分析了两异构分子在267nm的C—Br键解离通道.对于2-溴噻吩和3-溴噻吩,产物Br来源于三个通道:(i)从单重激发态系间窜跃到排斥的三重激发态的快速预解离;(ii)单重激发态内转化到高振动基态的热解离;(iii)母体分子多光子电离后的解离.2-溴噻吩的产物Br*具有类似的产生机制;但对于3-溴噻吩,从激发态内转换到高振动基态发生热解离成为产物Br*的主导通道,而来自激发三重态的快速预解离通道则几乎消失.定量地给出了各个通道的相对贡献、能量分配及各向异性分布信息.实验发现,随着溴原子在噻吩上取代位置远离硫原子,来自通道(i)和(ii)产物之间的比例明显减小,相应的各向异性分布有变弱趋势.C--Br bond dissociation mechanisms of 2-bromothiophene and 3-bromothiophene at 267 nm were investigated using ion velocity imaging technique. Translational energy distributions and angular distributions of the photoproducts, Br（^2P32） and Br^＊ （2p1/2）, were obtained and the possible dissociation channels were analyzed. For these two bromothiophenes, the Br fragments were produced via three channels： （i） the fast predissociation following the intersystem crossing from the excited singlet state to repulsive triplet state; （ii） the hot dissociation on highly vibrational ground state following the internal conversion of the excited singlet state; and （iii） dissociation following the multiphoton ionization of the parent molecules. Similar channels were involved for photoproduct Br^＊ of the 2- bromothiophene dissociation at 267 nm; while for the photoproduct Br^＊ of 3-bromothiophene, the dissociation channel via internal conversion from the excited singlet state to highly vibrational ground state became dominating and the fast predissociation channel via the excited triplet state almost disappeared. Informations about the relative contribution, energy disposal, and the anisotropy of each channel were quantitatively given. It was found that with the position of Br atom in the thienyl being far from S atom, the relative ratios of products from channels （i） and （ii） decreased obviously and the anisotropies corresponding to each channel became weaker.

关 键 词：溴噻吩 光解离 离子速度影像 

分 类 号：O641.1[理学—物理化学]