Femtosecond Studies of the Influence of Solvent on Chemical Reaction Dynamics

在这个由化学部化学结构动力学和机理（CDSM-A）项目资助的项目中，南加州大学的Stephen Bradforth教授正在使用光电子能谱（PES）和其他基于激光的技术来研究液氨的结构。PES是一种利用光从原子或分子中移除电子的技术。通过测量这些电子的能量，可以获得有关分子结构的信息，以及它与附近其他分子的相互作用。Bradforth小组也在研究当额外的电子溶解在液体中时，氨分子之间的相互作用会发生什么。之所以选择液态氨，是因为它可以溶解更高浓度的电子，其结构与水相似，而且氨与许多重要的工业过程有关。由于PES技术涉及从由光引起的分子中去除电子，因此该研究也可能为类似的过程提供见解，例如光对活细胞造成的损害（例如，在癌症放射治疗期间）。参与该项目的学生和博士后将接受有关新仪器制造仪器的培训，并从国际实验室的培训中受益。作为该项目更广泛影响的一部分，布拉德福斯教授正在继续开展一项外展项目，为少数族裔社区学院赛瑞都学院（Cerritos College）的学生提供暑期实习机会。本研究项目探讨了氢键液氨的电子结构，以及这种结构与水的电子结构的关系。该项目的一个中心焦点是确定溶质掺杂剂如何控制态的电子密度。该项目的具体目标是：(i)通过实验光电子能谱（PES）和光电子角分布（PAD）测量确定液价带轨道离域；（ii）利用泵浦探针PES测量含有溶剂化电子（由碱金属提供）的液氨，识别分离的溶剂化电子、自旋对双电子，以及在高过量电子浓度下的金属-绝缘体跃迁；（iii）利用连续双光子吸收光谱表征低洼导带态及其与局域分子门口态的耦合。瞬态吸收和光电子能谱的工作是在南加州大学Bradforth教授的实验室完成的。角度分辨可调x射线光电子能谱（PAD）研究是在汉堡和柏林同步加速器光源上进行的。

In this project funded by the Chemical Structure Dynamics and Mechanism (CDSM-A) program of the Chemistry Division, Professor Stephen Bradforth of the University of Southern California is using photo-electron spectroscopy (PES) and other laser-based techniques to study the structure of liquid ammonia. PES is a technique that uses light to remove electrons from an atom or molecule. By measuring the energy of these electrons, information can be obtained about the structure of the molecule as well as its interactions with other nearby molecules. The Bradforth group is also studying what happens to the interactions between ammonia molecules when extra electrons are dissolved in the liquid. Liquid ammonia was chosen because it can dissolve higher concentrations of electrons, is similar to water in its structure, and because ammonia is relevant to a number of important industrial processes. Since the PES technique involves removal of electrons from molecules caused by light, the research may also provide insights into similar processes such as the damage to living cells caused by light (for example, during cancer radiation therapy). Students and postdocs involved in the project receive training in building instrumentation for new instruments and benefit from training in international labs. As part of the broader impact of this project, Professor Bradforth is continuing an outreach project that provides hands-on summer internships for students from Cerritos College, a minority-serving community college.This research project explores the electronic structure of the hydrogen-bonding liquid ammonia, and the relationship of this structure to that of water. A central focus of the project is to establish how the electronic density of states can be manipulated by solute dopants. The specific objectives of the project are: (i) to determine the liquid valence band orbital delocalization from experimental photoelectron spectroscopy (PES) and photoelectron angular distribution (PAD) measurements; (ii) to identify isolated solvated electrons, spin-paired dielectrons, and the metal-insulator transition at high excess electron concentration using pump-probe PES measurements of liquid ammonia containing solvated electrons (supplied by alkali metals), and (iii) to characterize low-lying conduction band states and their coupling to localized molecular doorway states using continuous two-photon absorption spectroscopy. The transient absorption and photoelectron spectroscopy work is being done in Professor Bradforth's laboratory at USC. The angle-resolved tunable X-ray photoelectron spectroscopy (PAD) studies are being conducted at the Hamburg and Berlin synchrotron light sources.