Wang Yanmei, Zhang Song, Wei Zhengrong, Zheng Qiusha, Zhang Bing
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China.
J Chem Phys. 2006 Nov 14;125(18):184307. doi: 10.1063/1.2371033.
The photodissociation dynamics of tert-C(4)H(9)Br and iso-C(4)H(9)Br has been studied at 234 and 265 nm using two-dimensional velocity map imaging technique. The translational energy and angular distributions have been analyzed for Br, Br(), and tert-C(4)H(9) radical. The energy distribution of Br atom in the photodissociation of tert-C(4)H(9)Br is found to consist of two Gaussian components. The two components are correlated to two independent reaction paths on the excited potential energy surfaces: (1) the high-energy component from the prompt dissociation along the C-Br stretching mode and (2) the low-energy component from the repulsive mode along the C-Br stretching, coupled with some bending motions. For the energy distribution of Br() atom in the photodissociation of tert-C(4)H(9)Br, a third multiphoton dissociative ionization channel is observed at 265 nm in addition to the two energy components corresponding to channels (1) and (2). The energy distributions of Br and Br() atoms in the photodissociation of iso-C(4)H(9)Br can be fitted using only one Gaussian function indicating a single formation channel. Relative quantum yields for Br((2)P(32)) at 234 and 265 nm in the photodissociation of tert-C(4)H(9)Br are measured to be 0.76 and 0.65, respectively. For iso-C(4)H(9)Br, the measured value is Phi(234 nm)(Br)=0.81. The contribution of bending modes to Br and Br() is much more obvious in the photodissociation of tert-C(4)H(9)Br than in iso-C(4)H(9)Br.
利用二维速度映射成像技术研究了叔丁基溴（tert-C(4)H(9)Br）和异丁基溴（iso-C(4)H(9)Br）在234和265纳米处的光解离动力学。对溴原子（Br）、溴自由基（Br()）和叔丁基自由基（tert-C(4)H(9)）的平动能和角分布进行了分析。发现叔丁基溴光解离过程中溴原子的能量分布由两个高斯分量组成。这两个分量与激发势能面上的两个独立反应路径相关：（1）沿C-Br伸缩模式的快速解离产生的高能分量；（2）沿C-Br伸缩的排斥模式并伴有一些弯曲运动产生的低能分量。对于叔丁基溴光解离过程中溴自由基（Br()）的能量分布，除了对应于通道（1）和（2）的两个能量分量外，在265纳米处还观察到第三个多光子解离电离通道。异丁基溴光解离过程中溴原子和溴自由基（Br()）的能量分布仅用一个高斯函数就能拟合，表明只有一个形成通道。测量得到叔丁基溴在234和265纳米处光解离产生溴（(2)P(32)）的相对量子产率分别为0.76和0.65。对于异丁基溴，在234纳米处测得的溴的量子产率为Phi(234 nm)(Br)=0.81。弯曲模式对叔丁基溴光解离中溴原子和溴自由基（Br()）的贡献比对异丁基溴光解离的贡献要明显得多。
