Optical manipulation of electron photodetachment in aqueous halide solutions: verification of atom-electron contact pairs via pump-repump probe spectroscopy

电子转移（ET）反应在化学、生物学和物理学中普遍存在，但是大多数ET系统中的大量自由度使得难以获得对电荷转移过程的基本理解。因此，研究由原子反应物如卤化物水溶液组成的模型系统是有意义的。量子模拟预测了两个渠道的电荷转移到溶剂（CTTS）状态的卤化物水溶液中的电子释放：绝热分离出的最低CTTS状态通过弱结合卤素电子对，所谓的接触对，和一个不太有效的通道直接电子注入到溶剂中。我们在这个项目中的主要目标是更详细地了解电子光剥离在水卤化物，特别是验证和表征的预测原子-电子接触对。回想一下，由于720 nm附近的基态吸收带非常相似，因此很难区分原子-电子对和最终水合电子这两种物质。为此，我们计划将泵浦-再泵浦-探测（PReP）光谱与众所周知的泵浦-探测技术相结合。在PReP光谱中的二次激发允许弛豫途径的光学操纵，并且可以提供关于所涉及的中间体的新信息。电子光剥离将通过短的紫外泵浦脉冲来完成，并且随后的分离和溶剂化动力学将在从紫外到中红外的宽光谱区域内用飞秒探测脉冲来监测。测量将在不同温度下进行，以验证预测的接触对的结合能。

Electron transfer (ET) reactions are ubiquitous in chemistry, biology and physics, but the large number of degree of freedom in most ET systems makes it difficult to obtain a fundamental understanding of the charge transfer process. Therefore, it makes sense to study model systems that consist of atomic reactants as the aqueous halides. Quantum simulations predicted two channels for the electron release out of charge-transfer-to-solvent (CTTS) states of aqueous halide: adiabatic separation out of the lowest CTTS state via a weakly bound halogen-electron pair, the so called contact pair, and a less effective channel for direct electron injection into the solvent. Our main goal in this project is a more detailed understanding of the electron photodetachment in aqueous halides, and in particular the verification and characterization of the predicted atom-electron contact pair. It is recalled that it is difficult to distinguish the two species, the atom-electron pair and the final hydrated electron, because of the very similar ground state absorption band around 720nm. For this purpose, we plan to apply punip-repump-probe (PReP) spectroscopy in combination with the well-known pump-probe technique. The secondary excitation in the PReP spectroscopy allows an optical manipulation of the relaxation pathway and can provide novel information on the involved intermediates. The electron photodetachment will be accomplished by a short UV pump pulse and the following separation and solvation dynamics will be monitored in a broad spectral region from UV to middle-infrared with femtosecond probing pulse. The measurements will be conducted at various temperatures in order to verify the binding energy of the predicted contact pair.