Femtosecond Dynamics of Bimolecular Reactions

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Professor McDonald is funded by a grant from the Experimental Physical Chemistry Program to study the dynamics of chemical reaction processes on a time scale of approximately 250 femtoseconds, using time resolved spectroscopy with laser pulses of that length. The goal is to study the reaction in the time scale of the bond-making process itself. A van der Waals cluster containing one reactant and a nonreactive molecule that can be made into the other reactant by photodissociation provides a convenient definition of a zero of time for a bimolecular reaction. The reactions to be studied involve the addition of radicals and atoms H, Cl, Br, or methyl to small double-bonded molecules such as ethylene. Products formed in the reaction in a cooled molecular beam will be detected by femtosecond pump-probe laser fluorescence or by multiphoton-ionization with time-of-flight mass spectroscopy detection. %%% Very fast laser pulses will be used in a stroboscopic technique to study the reaction between two reactants to form new molecules. Starting with the reactants loosely bound in a cluster, a flash of light begins the reaction. The observations will be carried out with light pulsing at the time scale of the reaction process itself to see the making of a new bond in progress.