A Deep Dive into Electron-Neutral Interactions

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In this project, funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Caroline Chick Jarrold and her students at Indiana University are studying interactions between electrons and neutral molecules using several sophisticated experimental techniques that are based on the absorption and emission of light by the chemical compounds being studied. Electron-neutral interactions drive many important chemical and physical processes, yet they are difficult to explore experimentally. From a practical standpoint, controlling electrons is challenging because they are thousands of times lighter than atoms, which themselves are tiny particles, while at the same time, the electric charge carried by the electron makes it vulnerable to deflection by the earth’s magnetic field, among other weak influencing forces present in laboratory settings. Professor Jarrold overcomes these hurdles by preparing the free electrons in a controlled way, which is to target negatively charged molecules with a laser pulse that removes an electron with a known amount of energy, and in the desired proximity of a neutral target molecule. The array of molecules selected for study are chosen to sample a broad range of properties that affect their interactions with electrons. The experiments involve the novel use of photoelectrons as a tool for probing valence-bound, non-valence-bound, and temporary anion states of molecules and bimolecular complexes, with an emphasis on preparing and probing systems that do not neatly fall into any of these three categories. This project addresses several hypotheses involving the description of electron-driven chemistry, the increasingly complex landscape for electron-bimolecular interactions, and the rules that govern non-valence-bound anion lifetimes. Probing these systems experimentally with energy-selected electrons is achieved by detachment of anionic precursors, which provides a route to mapping the energy-dependence of electron-neutral interactions, some of which initiate electron-driven chemistry. Additional studies include fluorescence lifetime and dispersed fluorescence measurements on non-valence-bound excited states of anions. Interpretation of data collected on these complex and often transient species is supported by calculations conducted by collaborator Professor Thomas Sommerfeld of Southeastern Louisiana University, who has expertise in the theoretical treatment of non-valence states of anions. The broader impacts include a more complete picture of electron-driven chemical and physical processes, which is a prerequisite for controlling these processes. In addition, participants in this project receive well-rounded graduate or postdoctoral training in a range of techniques in chemical physics, coupled with ample professional development opportunities, in the laboratory of a PI with a deep commitment to diversity and equity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.