Kit H. Bowen, Jr. of Johns Hopkins University is supported by an award from the Chemical Structure, Dynamics, and Mechanism Program of the Chemistry Division to investigate, with his graduate, undergraduate, and high school researchers, a broad range of chemical topics using gas-phase, anion photoelectron spectroscopy. Systems under study include negative ions of bio-molecules, diffuse excess electron states, and species formed by electron-induced proton transfer. All of these are related to fundamental questions and issues in chemistry and related fields. The synergy between these experiments and the work of Bowen's theoretical colleagues leads to yet deeper insight into structural, dynamical, and mechanistic aspects of these problems.
This research expands the frontiers of knowledge in fields as diverse as mass spectrometry, oncology, electrochemistry, analytical chemistry, enzymology, and radiation chemistry/biology. It shows us how electrons interact with molecules and collections of molecules (clusters) and how the resultant anions interact with other molecules. This work contributes strongly to the education of graduate students and undergraduates. It also provides high school students with a glimpse into scientific research.
We have utilized negative ion photoelectron spectroscopy to study a wide variety of molecular and cluster anions. While it is poorly understood, the attachment of electrons to polar molecules and to aggregates of molecules (clusters) is an important process in gases, e.g., the atmosphere, and in solutions, where chemical synthesis is conducted. We have explored the proposed "doorway" mechanism, whereby the initial stage of electron attachment produces dipole bound states, which then transforms themselves into more typical valence anion states. In another study, we mapped the electrophilic properties of sub-units of DNA. Secondary electrons produced during gamma irradiation are known to interact with DNA and in some cases to cause strand breaks. Our startegy for contributing to the understanding of these important electrophilic processes was to first form the parent negative ions of various DNA sub-units and then measure how much energy was required to remove their electrons. One of the leading hypotheses of how enzymatic catalysis works is based on the strengths of low barrier (ionic) hydrogen bonds being large. Some, however, doubt that they could have the necessary strengths. We have shown that they in fact do. Chiral molecules are increasing important in catalysis. While chiral metal clusters have especially exciting possibilities, very few are known. We formed and characterized the structures of several inherently chiral, four-atom metal clusters. We also studied several novel molecular anion systems, including azobenzene anions, which can be induced to isomerize by photodetachment, and the molecular oxalic acid anion, which as a non-aromatic organic molecule was not expected to be able to support an excess negative charge. The above studies have helped to elucidate unresolved issues in a variety of fields including enzymology, radiation biology, catalysis, and astrophysics. Several graduate students were trained via this grant, and four received their PhD degrees in part because of work they did on these projects. We have also engaged middle school and high school students as well as college and university undergraduates in research by way of tours, demonstrations, and in some cases participation in research.