Femtosecond Studies of the Influence of Solvent on Chemical Reaction Dynamics

该奖项由化学学部化学结构、动力学和机制项目资助，南加州大学的斯蒂芬·布拉德福斯教授和研究生将研究水中的化学反应动力学。新的飞秒电子和光电子能谱将被用于揭示水中的电离、解离和质子耦合电子转移反应途径，以光化学中的酚类分子作为模型系统。苯酚和噻吩的氢原子解离和电离动力学与激发态水的反应动力学有许多相似之处，但附加了表面跳跃动力学，将通过新的分散瞬态吸收实验以30 fs时间分辨率从气相映射到体水相。这些将由一个新的液体时间分辨光电子能谱仪的建设补充，能够探测沿反应坐标的演变，通过光电子能量和角分布。液体喷射光谱仪的初始目标将是不同对称的无机阴离子的稳态角分布和时间分辨苯酚激发态化学。虽然这个研究项目特别关注水酚系统，但它将导致对溶剂运动和溶质反应性之间相互作用的深入了解，这将直接影响大多数化学家和生物化学家如何设计和/或模拟化学转化。杂环芳烃（包括DNA碱基）的光化学反应与溶液中酚类发色团的激发态途径有关。苯酚本身是蛋白质中酪氨酸侧链的直接模型，其中酪氨酸自由基通常是电子转移活性的重要中间体。新一代物理科学专业的学生将在新的物质光谱探针以及在该领域的前沿设计和分析实验方面获得重要的训练。这些技能将为他们在美国至关重要的科学技术领域以及学术研究领域的职业生涯做好准备。研究生和本科生将有机会相互学习，并与国际科学家合作。布拉德福斯研究小组还将参与南加州大学的推广工作，为社区学院的学生提供以能量转换为主题的暑期实习机会，这些学生为洛杉矶东南部县的西班牙裔人口提供服务。在参与项目的各级，将继续强调不同群体的广泛参与以及这些参与者之间的协作

In this award, funded by the Chemical Structure, Dynamics and Mechanisms Program of the Chemistry Division, Professor Stephen Bradforth of the University of Southern California and graduate students will study chemical reactions dynamics in water. Novel femtosecond electronic and photoelectron spectroscopies will be employed to unravel ionization, dissociation and proton-coupled electron transfer reaction pathways in water with photochemistry in the phenol family of molecules serving as model systems. The hydrogen atom dissociation and ionization dynamics of phenol and thiophenol, bearing many similarities in reaction dynamics to that of excited-state water but with additional surface-hopping dynamics, will be mapped from gas phase to bulk aqueous phase by new dispersed transient absorption experiments with 30 fs time resolution. These will be complemented by the construction of a new liquid time-resolved photoelectron spectrometer, capable of probing evolution along the reaction coordinate via the photoelectron energy and angular distribution. Initial targets for the liquid-jet spectrometer will be the steady-state angular distributions from inorganic anions of different symmetries and time-resolving phenol excited state chemistry.While this research project focuses specifically on the aqueous phenol system, it will lead to insights into the interplay between solvent motions and solute reactivity that directly impact how most chemists and biochemists design and/or model chemical transformations. The photochemistries of heterocyclic aromatics, including the DNA bases, have related excited state pathways to the phenolic chromophores in solution. Phenol itself is a direct model for tyrosine side chain in proteins where tyrosyl radicals are often significant intermediates in electron transfer activity. A new generation of physical science students will gain vital training in new spectroscopic probes of matter as well as designing and analyzing experiments at the cutting edge of the field. These skills will prepare them for careers in the vital US science and technology sector as well as academic research. Graduate and undergraduate students will have the opportunity to learn from each other and collaborate with international scientists. The Bradforth research group will also participate in outreach efforts at USC to provide hands-on energy-conversion themed summer internships for community-college students serving the largely Hispanic population in South Eastern Los Angeles County. Broad participation of different groups, and collaboration amongst those participants, will continue to be emphasized at all levels of involvement in the project