Ultraviolet relaxation dynamics of aniline, N, N-dimethylaniline and 3,5-dimethylaniline at 250 nm.
Ultraviolet relaxation dynamics of aniline, N, N-dimethylaniline and 3,5-dimethylaniline at 250 nm.
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DOI：
10.1063/1.4914330
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发表时间：
2015-03
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影响因子：
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通讯作者：
James O. F. Thompson;Lisa Saalbach;Stuart W Crane;M. Paterson;D. Townsend
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作者：
James O. F. Thompson;Lisa Saalbach;Stuart W Crane;M. Paterson;D. Townsend
利用时间分辨光电子成像技术研究了气相苯胺、N，N-二甲基苯胺和3，5-二甲基苯胺在250 nm紫外光激发下的电子弛豫动力学。我们的分析得到了支持的从头算耦合簇计算评估激发态能量和（在苯胺）的激发态物理性质的范围作为N-H键扩展的函数的演变。由于在苯胺中进行的几个早期研究之间缺乏一致性，本工作的具体目标是获得对先前提出的两个最低单重激发态S1（ππ（π））和S2（3s/πσ（π））之间的非绝热耦合相互作用的新见解。包括甲基取代的N，N-二甲基苯胺和3，5-二甲基苯胺，以获得关于驱动S1（ππ（π））/S2（3s/πσ（π））耦合机制的关键内部分子坐标的更详细的动力学信息。我们的研究结果表明，在所有三个系统中，两个电子态在初始激发期间被直接填充，S2（3s/πσ（π））态随后可能通过沿着N-X伸缩坐标（X = H或CH 3）的直接解离或内部转换到S1（ππ（π））态而衰减。在苯胺和N，N-二甲基苯胺中，两种途径最有可能竞争耗尽S2（3s/πσ（π））态。然而，在3，5-二甲基苯胺，只有直接解离机制似乎是活跃的。这是合理化的变化方面的两个衰变途径甲基化后的芳环系统的相对速率。
Time-resolved photoelectron imaging was used to investigate the electronic relaxation dynamics of gas-phase aniline, N, N-dimethylaniline, and 3,5-dimethylaniline following ultraviolet excitation at 250 nm. Our analysis was supported by ab initio coupled-cluster calculations evaluating excited state energies and (in aniline) the evolution of a range of excited state physical properties as a function of N-H bond extension. Due to a lack of consistency between several earlier studies undertaken in aniline, the specific aim of this present work was to gain new insight into the previously proposed non-adiabatic coupling interaction between the two lowest lying singlet excited states S1(ππ(∗)) and S2(3s/πσ(∗)). The methyl-substituted systems N, N-dimethylaniline and 3,5-dimethylaniline were included in order to obtain more detailed dynamical information about the key internal molecular coordinates that drive the S1(ππ(∗))/S2(3s/πσ(∗)) coupling mechanism. Our findings suggest that in all three systems, both electronic states are directly populated during the initial excitation, with the S2(3s/πσ(∗)) state then potentially decaying via either direct dissociation along the N-X stretching coordinate (X = H or CH3) or internal conversion to the S1(ππ(∗)) state. In aniline and N, N-dimethylaniline, both pathways most likely compete in the depletion of S2(3s/πσ(∗)) state population. However, in 3,5-dimethylaniline, only the direct dissociation mechanism appears to be active. This is rationalized in terms of changes in the relative rates of the two decay pathways upon methylation of the aromatic ring system.