In this project, supported by the Chemical Structure, Dynamics and Mechanisms Program of the Chemistry Division, Professor Sanov and his students will undertake a study of the structure and dynamics of negative ions in the gas phase. The broad objective of this research is to attain a molecular-level view of chemistry. As chemical bonding is controlled by electrons, it is their behavior that ultimately controls the outcomes of chemical reactions. The bonding motifs in molecular and cluster anions will be investigated using experimental techniques targeting electron emission and anionic fragmentation processes. In particular, a quantum photographic technique - photoelectron imaging - will be used to investigate the limits of through-space and through-bond electronic coherence, which is a cornerstone of many charge-transfer phenomena. The reactivity of selected neutral radicals and reactive intermediates, as well as the interactions of negative ions and photoelectrons with neighboring molecules in microscopic solvation environments (clusters) will also be studied.
The knowledge attained in this research is expected to be relevant to several areas of physical sciences. The properties of negative ions are vital to understanding chemistry of solutions, bio-, environmental, and astro-chemistry. For example, characterizing several carbon-rich species will shed light on the mechanisms of formation of negative ions in the Universe, while the studies of electronic coherence at the molecular level will help understand the fundamental factors controlling the flow of charges in molecules and devices. As part of the broader scientific community, the Sanov group will continue advancing the utility of photoelectron imaging in providing conceptual views of bonding structures, which ultimately hold matter together. The research will also contribute to the development of photoelectron imaging's untapped potential as an effective teaching tool, by providing a pedagogical framework for introducing students to quantum concepts.
The broadly defined objective of this research program is to attain a molecular-level view of the essence of chemistry: the behavior of electrons both in stable molecules and in molecules undergoing chemical change. As chemical bonding is controlled by electrons, it is their properties that control the molecular bonding structures and the outcomes of chemical reactions. The general directions of the completed project were threefold. First, the researchers in the Sanov group characterized the electronic structure of several important anions and the corresponding neutral molecules. Second, they studied the interactions of anions with neighboring molecules in microscopic solvation environments. Third, they advanced the fundamental understanding of the physics of photodetachment processes by contrasting the experimental observations with predictions of practical models that describe the photoelectron angular distributions. Negative ions are important in many natural and technological processes. Their properties are vital to understanding the chemistry of solutions, bio- and environmental chemistry. The anions targeted in this work are chosen not only for their fundamental properties, but also their practical significance. The main experimental method employed was photoelectron imaging spectroscopy, enhanced by time-of-flight mass-spectroscopic characterization of the precursor anions and their fragments. As part of this project, the Sanov group developed the utility of photoelectron imaging in the studies of the electronic structure, photodetachment, and time-resolved dynamics of molecular and cluster anions and focused considerable effort on understanding the experimental "signatures" of molecular orbitals. As specific examples, the project yielded important structural and thermochemical properties of several heterocyclic organic radicals (for example, furanyl, thiophenyl, oxazolyl), carbenes (e.g., dichloro- and dicyano-carbenes and the mixed chlorocyanocarbene), and strong electron acceptors (e.g., tetracyanoethylene). Photoelectron imaging was used to determine the electron affinities and the molecular-orbital properties of the reactive intermediates and the bond-dissociation energies of the corresponding closed-shell molecules. The resulting thermodynamical quantities were used to calculate the reaction energies and heats of formation of a variety of molecules within the self-consistent framework of thermodynamics. New breakthroughs have been achieved in developing the fundamentals of anion photodetachment. A particular important outcome is the new practical model (the mixed s-p model) for the understanding, conceptual interpretation and quantitative analysis of photoelectron angular distributions in the photodetachment from spn hybrid molecular orbitals, which are ubiquitous in organic chemistry. This model could provide a boost to the entire field of photoelectron imaging by enabling the researchers to obtain more relevant information from photoelectron images for molecular anions. The project yielded about 20 original research articles published in leading peer-reviewed journals. In addition to scientific output, this research program serves as a vehicle for academic and professional advancement of students and postdocs. During the previous funding period, three graduate students (two of whom are women) graduated with Ph.D. degrees. While at Arizona, all three received prestigous research awards. One graduate moved to a postdoctoral position at Max Planck Research Department for Structural Dynamics, University of Hamburg. Another graduate was awarded an ACS/AAAS Policy Fellowship and spent the subsequent 2011-2012 fiscal/academic year as a Congressional Fellow in Washington, D.C. Most recently, she was awarded another AAAS Science & Technology Policy Fellowship and now works at the NSF. The third, most recent Ph.D. graduate just recently started a postdoctoral appointment at Sandia, National Laboratories (Livermore).
