Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui, People's Republic of China.
J Chem Phys. 2011 Dec 28;135(24):244302. doi: 10.1063/1.3671368.
We report on the photodissociation dynamics of tert-pentyl bromide near 265 nm investigated by time-sliced velocity map imaging. The speed and angular distributions have been analyzed for both the ground-state Br((2)P(3∕2)) atom (denoted Br) and the spin-orbit excited-state Br((2)P(1∕2)) atom (denoted Br*). The speed distributions of Br and Br* atoms are all found to consist of three Gaussian components, which correlate to three independent dissociation pathways on the excited potential energy surfaces: (1) the high translational energy (E(T)) component from the prompt dissociation along the C-Br stretching mode, (2) the middle E(T) component from the repulsive mode along the C-Br stretching coupled with some bending motions, and (3) the low E(T) component from the repulsive mode along the C-Br stretching coupled with more bending motions. More interestingly, we have also observed the tert-C(5)H(11)(+) ions in 263-267 nm. The near-zero kinetic energy distributions extracted from the three tert-C(5)H(11)(+) images near 265 nm show the typical characteristics that are attributable to multiphoton dissociative ionization, suggesting the existence of a neutral superexcited state of the parent tert-pentyl bromide molecule. The contribution of bromine atoms formed in this dissociative ionization channel adds in the total relative distribution of low E(T) component in the Br*(Br) formation channel, which reasonably explains the abnormal distributions observed in between the middle and low E(T) components in the Br*(Br) formation channel.
我们报道了在 265nm 附近通过时间切片速度映射成像研究的叔戊基溴的光解动力学。分析了基态 Br((2)P(3∕2))原子（表示为 Br）和自旋轨道激发态 Br((2)P(1∕2))原子（表示为 Br*）的速度和角分布。发现 Br 和 Br原子的速度分布都由三个高斯分量组成，这与激发势能面上的三个独立解离途径相关：（1）沿 C-Br 伸缩模式的快速解离产生的高平移能量（E(T)）分量，（2）沿 C-Br 伸缩模式耦合一些弯曲运动的中等 E(T)分量，以及（3）沿 C-Br 伸缩模式耦合更多弯曲运动的低 E(T)分量。更有趣的是，我们还在 263-267nm 处观察到了叔-C(5)H(11)(+)离子。在 265nm 附近从三个叔-C(5)H(11)(+)图像中提取的近零动能分布显示出典型的特征，归因于多光子解离电离，表明母体叔戊基溴分子存在超激发态的中性。在这个解离电离通道中形成的溴原子的贡献增加了 Br(Br)形成通道中低 E(T)分量的总相对分布，这合理地解释了在 Br*(Br)形成通道中中低 E(T)分量之间观察到的异常分布。
