Abteilung für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstrasse 12, 53115 Bonn, Germany.
J Phys Chem B. 2013 Jul 25;117(29):8844-54. doi: 10.1021/jp404532s. Epub 2013 Jul 12.
We recently reported first femtosecond pump–probe experiments on the geminate recombination dynamics of solvated electrons in fluid ammonia (Urbanek et al., J. Phys. Chem. B 2012, 116, 2223–2233). The electrons were generated through a vertical two-photon ionization at a total energy of 9.3 eV. Here, we present a full Monte Carlo analysis of the time-resolved data to determine the solvated electron’s thermalization distance from the ionization hole, NH(3)(+). The simulations are compared with the experiment over wide thermodynamic conditions to obtain insight into the dependence of the vertical ionization mechanism on the electronic properties of the solvent network. The simulations reveal that the average thermalization distance, <r(0)>, decreases strongly with both increasing temperature, T, and decreasing density, ρ, from 3.2 nm in the cryogenic fluid down to roughly 0.5 nm in the dilute supercritical phase with almost gas-like densities. We combine our results with the current understanding of the T,ρ-dependence of the electronic structure of the liquid phase and discuss in detail the role of thermally induced energy level shifts for the valence-to-conduction band gap. The observed changes of the thermalization distance can be well attributed to a gradual decrease of the excess energy initially imparted on the ejected electron as gas-like conditions are progressively approached.
我们最近报道了首例飞秒泵浦-探测实验，研究了在液态氨中溶剂化电子的复合动力学（Urbanek 等人，J. Phys. Chem. B 2012, 116, 2223-2233）。电子是通过总能量为 9.3 eV 的垂直双光子电离产生的。在这里，我们对时间分辨数据进行了全面的蒙特卡罗分析，以确定溶剂化电子从电离空穴 NH(3)(+)热化的距离。模拟结果与实验在广泛的热力学条件下进行了比较，以深入了解垂直电离机制对溶剂网络电子性质的依赖性。模拟结果表明，平均热化距离 <r(0)> 随着温度 T 和密度 ρ 的增加而强烈减小，从低温流体中的 3.2nm 下降到稀超临界相中的约 0.5nm，密度几乎与气体相同。我们将我们的结果与对液相电子结构的 T、ρ 依赖性的现有理解相结合，并详细讨论了热诱导能级位移对价带到导带能隙的作用。热化距离的观察到的变化可以很好地归因于随着接近气体状条件，最初赋予被逐出电子的过剩能量逐渐减小。
