MPGMC · Ultrafast dynamics of chemical reactions in solution

Ultrafast dynamics of chemical reactions in solution

The aim of the originally proposed MPGMC project was to develop and carry out time-resolved spectroscopic experiments to link gas-phase and solution-phase chemistry, through a series of experiments designed to explore the effect of solvent on different classes of chemical and photochemical reactions. In the original proposal, we predicted the following 24 month timeline of activities 1-9, and are very pleased to report that all the proposed objectives have been addressed: 1,2. Building the spectrometer/Running test experiments: The transient spectroscopy laboratory has been constructed and tested, and now enjoys daily use by the MC Fellow (Dr. Grubb), three graduate students, and three post docs. The lab has also been used by visiting scientists from Kyoto University, the University of Wisconsin, Oxford, and Kiel University. 3. Photochemistry of Biologically Relevant Molecules: The photostability of the DNA base adenine was investigated using transient spectroscopy, and the chemical bonds were found to be stable to much higher energy photons than in the gas phase. An extension of this work to pairs of DNA bases, in collaboration with Kiel University, is currently underway. These studies may help elucidate some of the mechanisms by which biomolecules developed on the prebiotic Earth. 4. Reactions of CN atoms with Hydrocarbons in Various Solvents: An extensive longitudinal study has been performed observing CN reactions with hydrocarbons in many different solvent environments: chloroform, dichloromethane, methanol, acetonitrile, acetone, and tetrahydrofuran. Unique timescales for CN solvation, and subsequent reactions, are observable in each case. This is certainly one of the most comprehensive studies of the effect of solvent environment on the same reaction ever performed, and will be valuable for the development of theoretical models hoping to capture the properties of these common solvents. A manuscript describing this work is currently in preparation. 5. Ring-Opening Chemistry: The photolytic ring-opening dynamics of thiophenone and furanone were observed using transient spectroscopy. Ring-opening is a pathway to which our previous time-of-flight gas phase experiments have been blind, but is easily observable via the transient infrared spectrum. With the aid of ab initio calculations, we proposed a mechanism involving internal conversion from the initially excited nπ* state to a dark nσ* state and thence the ground state potential energy surface, which results in the observed ring-opening.

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