Femtosecond studies of the influence of solvent on chemical reaction dynamics

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In this award, funded by the Experimental Physical Chemistry program of the Chemistry Division, Professor Stephen Bradforth of the University of Southern California and graduate students will continue their investigation of liquid medium effects on photo-dissociation, explore new avenues in photo-initiated bimolecular reactions, and develop nonlinear optical spectroscopic techniques that can probe reactions at liquid surfaces. The photo-dissociation studies will focus on solvent effects on the dissociation of molecules such as ICN, BrCN and H2O2, and especially subsequent femtosecond time scale rotational relaxation of the diatomic fragments (CN and OH) produced in the dissociation. Comparison of experimental data with molecular dynamics simulations will aid in the evaluation of solvent effects on relaxation dynamics. The study of photo-initiated bimolecular reactions will involve photo-generation of OH radicals (from OH- or H2O2) and observation of their reaction with Cl- and Br- in the femtosecond regime. These radical-ion reactions are of emerging interest in atmospheric chemistry as possible routes to the formation of tropospheric Cl2 and Br2. Second order nonlinear optical techniques, which can provide surface-specific information, will be developed in order to explore reaction dynamics at liquid or aerosol particle surfaces. While the initial focus will be on solvation and mobility of photo-detached electrons, these techniques may eventually be applicable to the study of halogen formation reactions on sea-spray aerosols.In addition to the broad dissemination of research results through publications, conference and seminar presentations, Prof. Bradforth will also make available via his group website important innovations in instrumentation that may be useful to other groups working in ultrafast dynamics.