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

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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.