Electron and Positronium Collisions with Molecules

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Low-energy electrons and their antiparticles, positrons, play a critical role in a large number of fundamental and applied fields. Electrons can induce specific chemical reactions which are relevant to dielectric aging, surface engineering, radiation damage, cancer therapy, and atmospheric physics. Collisions involving positrons and positron-containing atoms play an important role in ongoing investigations of fundamental properties of matter and antimatter. Answers to the big question of why matter dominates over antimatter in our universe require studies of the simplest antimatter atom, antihydrogen. Creation of antihydrogen atoms can be accomplished by colliding antiprotons with positronium atoms, each containing an electron and a positron. These processes are currently investigated at the CERN laboratory in Switzerland, which provides the powerful source of antiprotons. This project will contribute to such efforts by providing a foundation of basic collision theory, and by extending existing collision theory into uncharted domains. The awarded research will have impact in the areas of chemical control, radiobiology, atmospheric science, and in studies of fundamental properties of antimatter. The research involves interdisciplinary efforts and international collaborations with scientists from other fields of physics and chemistry. Supervision of graduate students promotes their training in diverse areas of physics.The project involves studies of electron-molecule and positronium-molecule collision processes. These studies are supplemented by theoretical investigation of more fundamental processes of positronium collisions with protons and antiprotons. The research focus is on development of the theory of the dissociative electron attachment to polyatomic molecules, the process resulting in bond breaking in molecules and dissociating them into neutral and negatively charged fragments. Effective potentials are used for calculation of positronium collisions with diatomic molecules with emphasis on the resonant scattering. New quantum-mechanical methods for theoretical studies of positronium-proton/antiproton collisions are being developed and compared with results of previous classical simulations. The research activities advance the theory of electron and positronium interactions with molecules and protons/antiprotons. First, they develop new formalisms which are then applied to electron and positronium collisions with various targets. Second, they lead to generation of new data which promote understanding of these processes, particularly dissociative electron attachment processes and positronium-molecule elastic and inelastic collisions. Third, they determine the range of validity of classical methods for treatment of positronium-proton/antiproton collisions which were used in the past.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.