Wu Hua, Xue Yuanxin, Wen Junqing, Wang Hui, Bai Lihua, He Wanlin, Sun Ruijuan, Zheng Wenli
School of Sciences, Xi'an Shiyou University Shanxi 710065 P. R. China
RSC Adv. 2019 Oct 7;9(55):31853-31859. doi: 10.1039/c9ra07498h.
By using a dc-slice imaging technique, photodissociation of 1,2-CHBrCl was investigated at 800 nm looking for heteronuclear unimolecular ion elimination of BrCl in an 80 fs laser field. The occurrence of fragment ion BrCl in the mass spectrum verified the existence of a unimolecular decomposition channel of BrCl in this experiment. The relative quantum yield of the BrCl channel was measured to be 0.8%. By processing and analyzing the velocity and angular distributions obtained from the corresponding sliced images of BrCl and its partner ion CH , we concluded that BrCl came from Coulomb explosion of the 1,2-bromochloroethane dication 1,2-CHBrCl. With the aid of quantum chemical calculations at the M06-2X/def2-TZVP level, the potential energy surface for BrCl detachment from 1,2-CHBrCl has been examined in detail. According to the calculations, two transition state structures tended to correlate with the reactant 1,2-CHBrCl and the products BrCl + CH . In this entire dissociation process, the C-Br and C-Cl bond lengths were observed to elongate asymmetrically, that is, the C-Br chemical bond broke firstly, and subsequently a new Br-Cl chemical bond started to emerge while the C-Cl bond continued to exist for a while. Hence, an asynchronous concerted elimination mechanism was favored for BrCl detachment.
通过使用直流切片成像技术，在800纳米波长下对1,2 - CHBrCl的光解离进行了研究，以寻找在80飞秒激光场中BrCl的异核单分子离子消除过程。质谱中碎片离子BrCl的出现证实了本实验中存在BrCl的单分子分解通道。测得BrCl通道的相对量子产率为0.8%。通过处理和分析从BrCl及其伴随离子CH的相应切片图像获得的速度和角分布，我们得出结论，BrCl来自1,2 - 溴氯乙烷二价离子1,2 - CHBrCl的库仑爆炸。借助于M06 - 2X/def2 - TZVP水平的量子化学计算，详细研究了BrCl从1,2 - CHBrCl脱离的势能面。根据计算，两个过渡态结构倾向于与反应物1,2 - CHBrCl和产物BrCl + CH相关。在整个解离过程中，观察到C - Br和C - Cl键长不对称地伸长，即C - Br化学键首先断裂，随后新的Br - Cl化学键开始形成，而C - Cl键仍持续存在一段时间。因此，BrCl脱离过程倾向于一种异步协同消除机制。
