Department of Basic Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, 153-8902 Tokyo, Japan.
J Phys Chem A. 2012 Nov 26;116(46):11167-79. doi: 10.1021/jp304781m. Epub 2012 Jul 25.
We reexmine the mechanism and interpretation of photochemical reaction of phenol molecule with small ammonia clusters, which is schematically written as PhOH···(NH(3))(n) → PhO(•)···[H(NH(3))(n)](•) with n ≤ 5. The low-lying excited states of this system in the adiabatic representation are densely quasi-degenerate due to the presence of the Rydberg-like diffused states in ammonia clusters. To treat the dynamics on such highly quasi-degenerate electronic states, we have carried out a large scale semiclassical Ehrenfest dynamics, nonadiabatic electron wavepacket dynamics in terms of very many configuration-state functions, to track the nonadiabatic electron and proton transfer dynamics in the time step of attosecond scale, integrating up to 300 fs. It turns out that the mechanism is more complicated than that referred to as excited-state hydrogen-atom transfer, which is widely accepted now. The pathways of jumping electron and shifting proton nucleus are identified to be mutually different, which necessarily results in charge separation in ammonia clusters after the transitions. The global feature of the present transfer dynamics is fully analyzed as one of the general prototypes of coupled electron-proton transfer in excited states.
我们重新审视了苯酚分子与小氨分子簇光化学反应的机制和解释，其示意图为 PhOH···(NH(3))(n) → PhO(•)···[H(NH(3))(n)](•)，其中 n ≤ 5。由于氨分子簇中存在类 Rydberg 扩散态，该体系的低能激发态在绝热表示中是密集的准简并态。为了处理这些高度准简并电子态上的动力学，我们进行了大规模的半经典 Ehrenfest 动力学和非绝热电子波包动力学，涉及到非常多的组态态函数，以在阿秒尺度的时间步长上追踪非绝热电子和质子转移动力学，积分时间长达 300 fs。结果表明，该机制比现在广泛接受的激发态氢原子转移机制更为复杂。跳跃电子和移动质子核的途径是相互不同的，这必然导致氨分子簇在跃迁后发生电荷分离。我们对当前转移动力学的整体特征进行了全面分析，将其作为激发态中耦合电子-质子转移的一般原型之一。
