Wednesday, July 30, 2014

Getting to the shore when riding a wave from reactant to product

Suppose that you were trying to get across a floor that goes side to side like a wave goes up and down. If you started on the start line (call it the reactants), how long would it take you to cross to the finish line (call it the products) on the other side? In earlier work, we found “fixed” structures that could somehow tell you exactly when you were on the reactant and product sides even while the barrier was waving side to side. Just like you and I would avoid getting seasick while riding such a wave, the “fixed” structure has to move, but just not as much as the wave. So the structure of our dividing surface is “fixed” in the sense that our planet is always on the same orbit flying around the sun. This latter analogy can’t be taken too far because we know that our planet is thankfully stable. In the molecular case, the orbit is not stable. We just discovered that the rates at which molecular reactants move away from the dividing surface can be related to the reaction rate between reactant and products in a chemical reaction. (Note that the former rates are called Floquet exponents.) This is a particularly cool advance because we are now able to relate the properties of the moving dividing surface directly to chemical reactions, at least for this one simplified class of reactions.

The work involved a collaboration with Galen Craven from my research group and Thomas Bartsch from Loughborough University. The title of the article is "Communication: Transition state trajectory stability determines barrier crossing rates in chemical reactions induced by time-dependent oscillating fields.” The work was funded by the NSF, and the international partnership (Trans-MI) was funded by the EU People Programme (Marie Curie Actions). It was just released as a Communication at J. Chem. Phys. 141, 041106 (2014). Click on the JCP link to access the article.

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