Quantum chemical methods for studying photon and electron-driven processes

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Spiridoula Matsika of Temple University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop and apply theoretical methods to better understand electron-driven processes. Electrons are ubiquitous in nature. Collisions of electrons with atoms and molecules are essential in biology and chemistry, as well as in technology. Examples of electron-driven phenomena can be found in interstellar chemistry, radiation chemistry, environmental chemistry, stability of waste repositories, plasma processing of materials for microelectronic devices and other applications. A major complication in electron-driven processes is that the in that the states that are involved are meta-stable since they can lose the electron via a process known as autodetachment. Matsika and her research group develop quantum mechanical approaches to treat metastable states and their behavior in electron-driven processes. They apply these methods to better understand DNA damage by radiation.. Low energy electrons can cause DNA strands to break and thus the interaction of low energy electrons with DNA is of major importance. This research will be carried out by a research team involving collaboration of undergraduate and graduate students with postdoctoral associates.Electron-driven processes have several similarities to photo-initiated processes, and progress made by the Matsika group and others in the latter field can be used to enhance the tools available in the former processes. In both photo-initiated and electron-driven phenomena electronically excited states are generated which are far from equilibrium and short lived. Nonadiabatic events are crucial and conical intersections are the rule rather than the exemption in both cases. Specific goals of this work are: 1) Development of efficient multireference configuration interaction (MRCI) methods for metastable states. The complex absorbing potential (CAP) approach is used in combination with MRCI to obtain both the energies and lifetimes of these states. A combination of conventional MRCI methods and CAP/MRCI are used to study potential energy surfaces, conical intersections, and nonadiabatic events related to resonances. 2) Theoretical studies of dissociative electron attachment (DEA) in nucleobases using the approaches developed in part (1). In order to address DEA in nucleobases the resonances are identified first, followed by explorations of the pathways leading to DEA and the experimentally observed products. The methodology developed will be implemented in publicly available computational software.