Yamamoto Yo-Ichi, Suzuki Toshinori
Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-Ku, Kyoto 606-8502, Japan.
J Phys Chem A. 2023 Mar 23;127(11):2440-2452. doi: 10.1021/acs.jpca.2c08046. Epub 2023 Mar 14.
Time-resolved photoelectron spectroscopy (TRPES) enables real-time observation of ultrafast electronic dynamics in solutions. When extreme ultraviolet (EUV) probe pulses are employed, they can ionize solutes from all electronic states involved in the dynamics. However, EUV pulses also produce a strong ionization signal from a solvent that is typically 6 orders of magnitude greater than the pump-probe photoelectron signal of solutes. Alternatively, UV probe pulses enable highly sensitive and selective observation of photoexcited solutes because typical solvents such as water are transparent to UV radiation. An obstacle in such UV-TRPES measurements is spectral distortion caused by electron scattering and a yet to be identified mechanism in liquids. We have previously proposed the spectral retrieval (SR) method as an approach to removing the distortion and overcoming this difficulty in UV-TRPES; however, its accuracy has not yet been verified by comparison with EUV-TRPES results. In the present study, we perform EUV-TRPES for charge transfer reactions in water, methanol, and ethanol, and verify SR analysis of UV-TRPES. We also estimate a previously undetermined energy-dependent intensity factor and expand the basis sets for SR analysis. The refined SR method is employed for reanalyzing the UV-TRPES data for the formation and relaxation dynamics of solvated electrons in various systems. The electron binding energy distributions for solvated electrons in liquid water, methanol, and ethanol are confirmed to be Gaussian centered at 3.78, 3.39, and 3.25 eV, respectively, in agreement with Nishitani et al. [ 2019, 5(8), eaaw6896]. An effective energy gap between the conduction band and the vacuum level at the gas-liquid interface is estimated to be 0.2 eV for liquid water and 0.1 eV for methanol and ethanol.
时间分辨光电子能谱（TRPES）能够实时观测溶液中的超快电子动力学。当使用极紫外（EUV）探测脉冲时，它们可以使参与动力学过程的所有电子态的溶质发生电离。然而，EUV脉冲也会从溶剂中产生强烈的电离信号，该信号通常比溶质的泵浦 - 探测光电子信号大6个数量级。另外，紫外探测脉冲能够对光激发的溶质进行高灵敏度和高选择性的观测，因为诸如水等典型溶剂对紫外辐射是透明的。这种紫外TRPES测量中的一个障碍是由电子散射以及液体中一种尚未确定的机制引起的光谱畸变。我们之前提出了光谱检索（SR）方法，作为一种消除畸变并克服紫外TRPES中这一困难的方法；然而其准确性尚未通过与EUV - TRPES结果进行比较来验证。在本研究中，我们对水、甲醇和乙醇中的电荷转移反应进行了EUV - TRPES实验，并验证了紫外TRPES的SR分析。我们还估计了一个先前未确定的能量相关强度因子，并扩展了用于SR分析的基组。改进后的SR方法被用于重新分析各种体系中溶剂化电子形成和弛豫动力学的紫外TRPES数据。液态水、甲醇和乙醇中溶剂化电子的电子结合能分布被证实为高斯分布，其中心分别位于3.78、3.39和3.25 eV，这与西谷等人[2019, 5(8), eaaw6896]的研究结果一致。气 - 液界面处导带与真空能级之间的有效能隙估计对于液态水为0.2 eV，对于甲醇和乙醇为0.1 eV。
