Beckman Fellow 1995-96

Martin Gruebele


Novel Effects in Vibrational Energy Redistribution: Theory and Experiment

Intramolecular vibrational energy redistribution (IVR) is an important and well-studied phenomenon which governs the flow of energy within molecules. This process affects the specificity with which molecules react, since reactivity depends on how molecular energy is localized in--or delocalized among--atom-atom bonds.Since understanding and controlling the reactivity of molecules is one of the main goals of physical chemistry, a detailed understanding of IVR is one of its "holy grails." While much progress beyond simple phenomenological theories has been made in recent years, many regimes of IVR remain poorly understood.

Professor Guebele's approach is twofold: 1) development of a new simple global model for IVR which retains the important physics and can easily be related to the available experimental spectroscopic information on molecules and 2) development of experiments which can test any "unusual" predictions of this model. Novel behavior in IVR may open a door to easier manipulation of complex chemical reactions.

So far, the model agrees with available experimental and theoretical evidence on hydrogen atom stretches (C-H or C-O bonds), where classic theory seems to hold up well. For different kinds of motions, which are far more common and important in most molecules (involving carbon, oxygen, and nitrogen stretching and bending motions), and have been less studied, the model predicts unexpected IVR behavior which differs qualitatively from accepted theories.

Professor Gruebele proposes to test this model on a large number of molecules, to see whether its new predictions are, in fact, universal. He will also include molecule-laser interactions in the calculations to predict experimental studies. A combination of ultrafast (femtosecond) and high-resolution laser techniques will be used to probe the new regimes of IVR in specific molecules. As a final step, chemically selective control by manipulation of IVR will be attempted.