Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California, 90095-1569, USA.
J Chem Phys. 2017 Aug 21;147(7):074503. doi: 10.1063/1.4985905.
We use one-electron non-adiabatic mixed quantum/classical simulations to explore the temperature dependence of both the ground-state structure and the excited-state relaxation dynamics of the hydrated electron. We compare the results for both the traditional cavity picture and a more recent non-cavity model of the hydrated electron and make definite predictions for distinguishing between the different possible structural models in future experiments. We find that the traditional cavity model shows no temperature-dependent change in structure at constant density, leading to a predicted resonance Raman spectrum that is essentially temperature-independent. In contrast, the non-cavity model predicts a blue-shift in the hydrated electron's resonance Raman O-H stretch with increasing temperature. The lack of a temperature-dependent ground-state structural change of the cavity model also leads to a prediction of little change with temperature of both the excited-state lifetime and hot ground-state cooling time of the hydrated electron following photoexcitation. This is in sharp contrast to the predictions of the non-cavity model, where both the excited-state lifetime and hot ground-state cooling time are expected to decrease significantly with increasing temperature. These simulation-based predictions should be directly testable by the results of future time-resolved photoelectron spectroscopy experiments. Finally, the temperature-dependent differences in predicted excited-state lifetime and hot ground-state cooling time of the two models also lead to different predicted pump-probe transient absorption spectroscopy of the hydrated electron as a function of temperature. We perform such experiments and describe them in Paper II [E. P. Farr et al., J. Chem. Phys. 147, 074504 (2017)], and find changes in the excited-state lifetime and hot ground-state cooling time with temperature that match well with the predictions of the non-cavity model. In particular, the experiments reveal stimulated emission from the excited state with an amplitude and lifetime that decreases with increasing temperature, a result in contrast to the lack of stimulated emission predicted by the cavity model but in good agreement with the non-cavity model. Overall, until ab initio calculations describing the non-adiabatic excited-state dynamics of an excess electron with hundreds of water molecules at a variety of temperatures become computationally feasible, the simulations presented here provide a definitive route for connecting the predictions of cavity and non-cavity models of the hydrated electron with future experiments.
我们使用单电子非绝热混合量子/经典模拟来研究基态结构和水合电子激发态弛豫动力学随温度的变化。我们比较了传统腔模型和水合电子最近的非腔模型的结果，并对未来实验中区分不同可能结构模型做出了明确的预测。我们发现，在恒定密度下，传统腔模型的结构没有随温度变化，导致预测的共振拉曼光谱基本上与温度无关。相比之下，非腔模型预测水合电子的共振拉曼 O-H 伸缩随温度蓝移。腔模型中不存在随温度变化的基态结构变化也导致了水合电子光激发后激发态寿命和热基态冷却时间随温度变化很小的预测。这与非腔模型的预测形成鲜明对比，在非腔模型中，激发态寿命和热基态冷却时间都预计会随温度显著降低。这些基于模拟的预测应该可以通过未来的时间分辨光电子能谱实验的结果直接验证。最后，两个模型预测的激发态寿命和热基态冷却时间随温度的差异也导致了水合电子作为温度函数的泵浦-探测瞬态吸收光谱的不同预测。我们进行了这样的实验，并在论文 II [E. P. Farr 等人，J. Chem. Phys. 147, 074504 (2017)]中进行了描述，发现激发态寿命和热基态冷却时间随温度的变化与非腔模型的预测非常吻合。特别是，实验揭示了从激发态的受激发射，其幅度和寿命随温度降低，这与腔模型预测的缺乏受激发射形成对比，但与非腔模型一致。总的来说，在描述具有数百个水分子的过剩电子的非绝热激发态动力学的从头计算在计算上变得可行之前，这里提出的模拟为将腔模型和水合电子的非腔模型的预测与未来的实验联系起来提供了一个明确的途径。
