Hydrogen Bonding, Proton Transfer, and Clusters on the Brink of Chemical Change

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In this project funded by the Chemical Structure, Dynamics, and Mechanisms A Program of the Chemistry Division, Professor Kenneth R. Leopold at the University of Minnesota performs fundamental studies on the forces of attraction between molecules. These forces are ubiquitous in nature and their study underlies our understanding a wide variety of chemical phenomena. The work is done by creating small clusters of two or three molecules and studying their physical properties. By grouping only a few molecules at a time, the simplification needed to fully understand the attractive forces is achieved. This work identifies prototypical systems that provide the most useful basic information. Whenever possible, prototypes are chosen that contain molecules known or suspected of being active in the Earth's atmosphere, thus providing foundational knowledge for atmospheric science. The direct focus on atmospherically important problems produces basic information needed to rationally evaluate the impact of both natural and anthropogenic changes to the environment. Additional impact is realized in the education of students and postdoctoral fellows who work on these problems. This project continues to grow a broader set of collaborators at Primarily Undergraduate Institutions (PUIs). The ability to collect a data in a short time is conducive to allowing undergraduate students the opportunity to see a project through from beginning to end. Microwave spectroscopy in a supersonic jet is used to determine molecular and electronic structure in small weakly bound complexes. Studies include complexes containing sulfur trioxide, carboxylic acids, sulfuric acid, and/or amines. Special emphasis is placed on systems that are on the brink of chemical reaction. Proton transfer, for example, is one common theme and its study provides a glimpse of the role of solvation in promoting chemical change. Quantum mechanical tunneling, when observed, offers experimental benchmarks with which to challenge theoretical chemical dynamics. Three-dimentional printing is explored as a convenient and inexpensive means of optimizing the design of the supersonic nozzles used to generate the chemical species of interest. The broader impact of this work lies, in part, in its elucidation of the fundamental interactions that govern solvation and determine the properties of matter. The understanding obtained informs fields as diverse as molecular biology and environmental science. Additional impact is derived from the training of graduate, undergraduate, and postdoctoral students that it provides.