Ned Sibert

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B.A. 1978, Colgate University                           
Ph.D. 1983, University of Colorado

Director, Theoretical Chemistry Institute

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Research Description

The long-term goal of our research is to develop predictive theories for the nuclear dynamics of small to medium size molecules in order that we may determine the dynamics of laser initiated chemical events. Working towards this goal our research focuses on theoretically describing the dynamics and spectroscopy of polyatomic molecules in both the gas and condensed phases. In the gas phase, we are interested in understanding the dynamics of proton transfer reactions, dynamics occurring on multiple potential surfaces, and the photodissociation of hydrogen bonded molecules. In the liquid phase we are investigating vibrational relaxation of CH and OH stretches due to the interplay of solvent-solute interactions and intramolecular couplings.

At low energies the dynamics in the gas phase is well understood. The rotational and vibrational motions are separable, and the vibrations consist of independent normal mode harmonic oscillators. At higher energies, that are relevant to chemical dynamics, the coupling between these motions becomes appreciable, mixing occurs as Fermi and Coriolis resonance interactions become prevalent. The resultant energy flow between the normal modes can be both rapid and complex. Our group develops the theoretical tools that allow us to probe these higher energy regimes.

The exact quantum mechanical solutions to the dynamics over a wide range of energies, using standard basis set methodologies, are intractable for systems with more than three degrees of freedom; hence alternative routes to their solutions must be explored and developed. One approach, that we have successfully pursued, is the implementation of perturbation theory to reduce the complexity of the problem. This approach not only allows us to describe many experimental spectra, but it also enables us to understand the spectra in terms of features in the classical phase space structures. With these methods we have begun to understand the dynamics of molecules whose energies span from the normal mode regime to the statistical region.

Vibrational relaxation in the condensed phase is relevant to many aspects of chemistry, physics, and biology. It is involved in thermal chemistry, shock-induced chemistry, electron transfer, photochemistry, and biological processes such as vision and photosynthesis. Vibrationally excited solute molecules relax due to solvent-solute interactions; thus the rate of energy transfer is a probe of these interactions. We are investigating the role of the CH and OH stretch relaxation in a variety of systems in order to unravel the multiple relaxation pathways that are available to solute molecules and to develop the theoretical tools that will enable us to combine quantum descriptions of the solute with classical descriptions of the solvent.

Awards and Honors

Fellow, American Chemical Society 2017
UW-Madison Chancellor's Distinguished Teaching Award 2013
James Taylor Excellence in Teaching Award, UW-Madison Department of Chemistry 2002
Villas Associate, University of Wisconsin-Madison 2002
National Science Foundation Presidential Young Investigator, University of Wisconsin-Madison 1989