Ward H. Thompson

Associate Professor

1251 Wescoe Hall Drive Malott Hall, Room 6079 University of Kansas Lawrence, KS 66045 Phone: (785) 864-3980 Fax: (785) 864-5396 Email: wthompson@ku.edu

Theoretical Physical Chemistry, reaction dynamics, quantum mechanical effects, energy transfer, proton transfer, spectroscopy, solvation effects, nanostructured materials.

Our research focuses on the development and application of theoretical methods for describing reaction dynamics, energy transfer, and spectroscopy in condensed phase systems. The emphasis is on understanding at a molecular level the fundamental behavior of interesting chemical systems and phenomena. The goal of our work is to develop accurate theoretical and computational approaches that can be feasibly applied to complex chemical problems including reactions in liquids and nanostructured environments. Some of the specific problems we are addressing are outlined below.

Reactions and Spectroscopy in Nanostructured Porous Materials.  Nanometer-sized cavities and pores can now be routinely generated in sol-gels, supramolecular assemblies, reverse micelles, zeolites, and even proteins, giving strong impetus to improving our understanding of chemistry in confined solvents. These cavities and pores can serve as nanoscale reaction vessels in which a chemical reaction takes place in the small pool of solvent allowed in the restricted space. One ultimate goal is to control the chemistry occurring in these systems by manipulating the properties of the confining framework as well as the species present. However, there is currently little understanding about how these properties affect chemical reactivity. We are addressing this issue using theoretical and computational approaches, within which the cavity/pore properties can be readily varied and the changes in reactivity directly examined. We are studying the energetics and dynamics of spectroscopy and chemical reactions in solvents confined within nanoscale frameworks using both simple models and atomistic models of silica pores (a snapshot of ethylene glycol confined in a hydrophilic silica pore is shown at right).  The fundamental question we are addressing is How does a reaction occur differently in a confined solvent than in a bulk solvent?  Charge transfer processes are typically strongly coupled to the solvent and are therefore dramatically affected by the limited number of solvent molecules, geometric constraints, and surface hydrophilicity/hydrophobicity. Thus, we are investigating proton transfer reactions, charge transfer spectra, and isomerization reactions.  By understanding how reactivity is connected to the pore characteristics, these studies will assist in the development of design principles for microporous and mesoporous catalysts.

Vibrational Relaxation in Bulk and Nanoconfined Liquids. It is difficult to overestimate the importance of vibrational relaxation since it plays a critical role in almost all aspects of chemistry (e.g., reaction dynamics and photochemistry). The timescale for vibrational relaxation ranges from ~10^-12 seconds to ~1 second, indicating the diversity of mechanisms and the challenges in understanding and treating relaxation dynamics. We are developing new simulation and theoretical methods that provide detailed insight into the molecular-level mechanisms of vibrational relaxation and spectral shifts and practical techniques for calculating relaxation rate constants. Specifically, we are using a mixed quantum-classical molecular dynamics approach in which the solute vibration(s) are treated quantum mechanically with the vibrationally adiabatic vibrational states calculated “on the fly” and the remaining degrees-of-freedom are described classically. Within these simulations the contributions to vibrational frequency shifts and vibrational relaxation of each solvent atom or molecule can be obtained to provide direct insight into the mechanisms of these processes. Concurrently, we are developing new statistical theoretical approaches for calculating vibrational relaxation.  We are applying these approaches to both bulk liquid systems and liquids confined in nanoscale pores.  In the latter we are gaining insight into how the vibrational spectra or relaxation rate constant, common experimental probes for characterizing porous materials, correspond to the microscopic structure and dynamics of the confined liquid.

Selected publications

Katie R. Mitchell-Koch and Ward H. Thompson, “How Important is Entropy in Determining the Position-Dependent Free Energy of a Solute in a Nanoconfined Solvent?” J. Phys. Chem. C 111, 11991-12001 (2007).

Brian B. Laird and Ward H. Thompson, “On the Connection between Gaussian Statistics and Excited-State Linear Response for Time- Dependent Fluorescence,” J. Chem. Phys. 126, 211104 (2007).

Christine M. Morales and Ward H. Thompson, “A Mixed Quantum-Classical Molecular Dynamics Analysis of the Molecular- Level Mechanisms of Vibrational Frequency Shifts,” J. Phys. Chem. A 111, 5422-5230 (2007).

Tolga S. Gulmen and Ward H. Thompson, “Testing a Two-State Model of Nanoconfined Solvents: The Conformational Equilibrium of Ethylene Glycol in Amorphous Silica Pores,” Langmuir 22, 10919 (2006).

Ward H. Thompson, “Proton Transfer in Nano-confined Polar Solvents. II. Adiabatic Proton Transfer Dynamics,” J. Phys. Chem. B 109 , 18201-18208 (2005).

J. A. Gomez, Ashley K. Tucker, Tricia D. Shepherd, and Ward H. Thompson, “Conformational Free Energies of 1,2-Dichloroethane in Nanoconfined Methanol,” J. Phys. Chem. B 109 , 17479-17487 (2005).

Ward H. Thompson, “Simulations of Time-Dependent Fluorescence in Nano-Confined Solvents,” J. Chem. Phys. 120 , 8125-8133 (2004).

Shenmin Li and Ward H. Thompson, “Simulations of the Vibrational Relaxation of I 2 in Xe,” J. Phys. Chem. A 107 , 8696-8704 (2003).

Ward H. Thompson, “A General Method for Implementing Vibrationally Adiabatic Mixed Quantum-Classical Simulations,” J. Chem. Phys. 118 , 1059-1067 (2003).