Femtosecond Nonlinear Spectroscopic Studies of Chemical Reactions in Condensed Phases

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In this project supported by the Experimental Physical Chemistry Program of the Chemistry Division, Jonas will study the elementary steps of chemical reactions in solution. Two new types of multiple-pulse femtosecond nonlinear spectroscopy will be developed in order to resolve the dynamics beneath the featureless spectra of molecules in liquids. One technique will use a three-pulse sequence to prepare and study transition states for thermally activated chemical reactions with a time resolution on the order of 20 femtoseconds. The second method will obtain the complete electric field information from four-wave mixing signals such as the photon echo by heterodyne detection using spectral interferometry. Experiments will study the role of the solvent in the unimolecular ionic dissociation of alkyl iodides with the aim of determining whether unimolecular ionic dissociation is activated by solvent fluctuations or intramolecular vibrational excitation. Solvents have dramatic effects on the rates of chemical reactions. They do this by altering the internal energy structure of solute molecules, changing the reaction mechanisms, or allowing new reaction paths. In this project two new experimental techniques will be used in experiments which are designed to probe the effect of solvents on a few different types of reactions, such as those which are expedited by increasing temperature. The results of these studies should help us understand how important solvent effects are in these different reactions. Such knowledge can help determine the conditions under which reactions in solution should be run for optimal desired results.