Photodissociation and Reaction Dynamics of Molecular and Cluster Anions Using Femtosecond Photoelectron Spectroscopy

加州大学伯克利分校的丹·纽马克支持这项研究， 实验物理化学计划和办公室 多学科活动，以利用他新开发的时间解决 实验技术，负离子飞秒光电子能谱 （FPES）研究光解离和反应动力学 负离子 具体来说，他将使用这种方法来探测 控制光解和双分子作用的势能面 反应过程中的孤立和集群的负离子。 的阴离子 FPES，飞秒（fs）泵浦激光器将负离子激发到 解离电子态;由此产生的演化系统是 用fs探测脉冲进行光分离， 测定了 光电子能谱与泵浦-探测延迟的关系 产生由探测脉冲引发的动态图像。 Neumark 首先将FPES应用于分离的阴离子，然后应用于阴离子 发色团在大小选择集群。 待调查的系统 包括用二氧化碳溶剂化碘二聚体阴离子簇，或 水、裸露或簇合的碘三聚体阴离子、臭氧阴离子和碳酸根 阴离子和时间分辨阴离子分子反应。 负离子在大气和溶液中起着重要的作用 化学. 这项研究的结果将立即应用于 化学动力学和光谱学，以及随后在 模拟广泛的物理化学现象，如大气 光和无线电频率波的污染和传播 正常和扰动的大气层。 此外，这些研究还应 对溶液中化学反应性质的新认识， 这些方法最终可能在蛋白质动力学的研究中具有实用性。

Dan Neumark of the University of California at Berkeley is supported by the Experimental Physical Chemistry Program and the Office of Multidisciplinary Activities to use his newly developed time-resolved experimental technique, anion femtosecond photoelectron spectroscopy (FPES) to investigate the photodissociation and reaction dynamics of negative ions. Specifically, he will use this method to probe the potential energy surfaces governing photodissociation and bimolecular reaction processes in isolated and clustered negative ions. In anion FPES, a femtosecond (fs) pump laser excites a negative ion to a dissociative electronic state; the evolving system that results is photodetached with a fs probe pulse and the photoelectron spectrum is measured. The photoelectron spectrum as a function of pump-probe delay yields a picture of the dynamics initiated by the probe pulse. Neumark will first apply FPES to the isolated anion, then to the anion chromophore in a size-selected cluster. Systems to be investigated include clusters of iodine dimer anions solvated with carbon dioxide or water, bare or clustered iodine trimer anions, ozone anions and carbonate anions, and time-resolved anion-molecule reactions. Negative ions play important roles in atmospheric and solution phase chemistry. Results of this research will find immediate application in chemical kinetics and spectroscopy, with subsequent application in modeling a wide range of physico-chemical phenomena, such as atmospheric pollution and transmission of optical and radio frequency waves in the normal and perturbed atmosphere. In addition, these studies should shed new light on the nature of chemical reactions in solution, and the methods may eventually be of utility in the study of protein dynamics.