Department of Physical Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany.
Acc Chem Res. 2012 Jan 17;45(1):131-8. doi: 10.1021/ar200170s. Epub 2011 Dec 21.
The solvation dynamics and reactivity of localized excess electrons in aqueous environments have attracted great attention in many areas of physics, chemistry, and biology. This manifold attraction results from the importance of water as a solvent in nature as well as from the key role of low-energy electrons in many chemical reactions. One prominent example is the electron-induced dissociation of chlorofluorocarbons (CFCs). Low-energy electrons are also critical in the radiation chemistry that occurs in nuclear reactors. Excess electrons in an aqueous environment are localized and stabilized by the local rearrangement of the surrounding water dipoles. Such solvated or hydrated electrons are known to play an important role in systems such as biochemical reactions and atmospheric chemistry. Despite numerous studies over many years, little is known about the microscopic details of these electron-induced chemical processes, and interest in the fundamental processes involved in the reactivity of trapped electrons continues. In this Account, we present a surface science study of the dynamics and reactivity of such localized low-energy electrons at D(2)O crystallites that are supported by a Ru(001) single crystal metal surface. This approach enables us to investigate the generation and relaxation dynamics as well as dissociative electron attachment (DEA) reaction of excess electrons under well-defined conditions. They are generated by photoexcitation in the metal template and transferred to trapping sites at the vacuum interface of crystalline D(2)O islands. In these traps, the electrons are effectively decoupled from the electronic states of the metal template, leading to extraordinarily long excited state lifetimes on the order of minutes. Using these long-lived, low-energy electrons, we study the DEA to CFCl(3) that is coadsorbed at very low concentrations (∼10(12) cm(-2)). Using rate equations and direct measurement of the change of surface dipole moment, we estimated the electron surface density for DEA, yielding cross sections that are orders of magnitude higher than the electron density measured in the gas phase.
在物理、化学和生物学的许多领域，局域过剩电子在水相环境中的溶剂化动力学和反应性引起了极大的关注。这种多方面的吸引力源于水作为溶剂在自然界中的重要性，以及低能电子在许多化学反应中的关键作用。一个突出的例子是电子诱导的氯氟碳化物（CFCs）的解离。低能电子在核反应堆中发生的辐射化学中也至关重要。水相环境中的过剩电子通过周围水分子偶极子的局部重排而被局域稳定。这种溶剂化或水合电子已知在生化反应和大气化学等系统中发挥重要作用。尽管多年来进行了许多研究，但对于这些电子诱导的化学过程的微观细节知之甚少，人们对涉及俘获电子反应性的基本过程的兴趣仍在继续。在本综述中，我们介绍了在 Ru(001)单晶金属表面支撑的 D(2)O 微晶上对这种局域低能电子的动力学和反应性的表面科学研究。这种方法使我们能够在明确定义的条件下研究过剩电子的产生和弛豫动力学以及电子附加分解（DEA）反应。它们是通过金属模板中的光激发产生的，并转移到晶体 D(2)O 岛的真空界面处的捕获位点。在这些陷阱中，电子与金属模板的电子状态有效地解耦，导致激发态寿命长达数分钟。利用这些长寿命、低能电子，我们研究了在极低浓度（约 10(12) cm(-2))共吸附的 CFCl(3)的 DEA。使用速率方程和表面偶极矩变化的直接测量，我们估计了 DEA 的电子表面密度，得到的截面比在气相中测量的电子密度高几个数量级。
