RUI: Photoionization, Time Delay, Positronium Formation, and Ion Impact Studies of Fullerenes, Endofullerenes, and Atoms

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By shining the laser light on an atom or by colliding the atom with charged particles one can probe the atom's response to such external stimuli. These are powerful scientific methods to learn fundamental properties of materials. Using these techniques to systems more complex than atoms and of direct applied interest is therefore beneficial for the advancement of basic science and technology. The systems to be studied in the current research are Buckminster fullerenes and other larger fullerenes, including atoms/clusters caged inside these molecules, called endofullerenes. These materials hold the promise of exciting applications in areas including quantum computations, superconductivity, biomedical fields, drug delivery research, magnetic resonance imaging, and organic photovoltaics. Hence, understanding the physical and chemical structure and response properties of these systems, including the influence of the fullerene cage on the behavior of the confined species, are matters of great scientific interest. Using large scale computer simulations the program aims to investigate how electrons inside the systems collectively interacts with each other to move internally or to exit the system and how much time they spend to reach the detector. How do the structure and geometry of the system play roles in the mechanism? This will be investigated both for light and fast-ion impact. By choosing exotic antiparticles like positrons to impact on fullerenes the study of the formation of electron-positron pairs, the positronium, is a novel direction of the program.Numerical methods to be employed to model the systems and their response are based on Density Functional Theory. These methods will also be used to calculate the intensity of the emerging electron flux from the system along a specific direction and/or in all directions. From the complex variation of the detected electron flux as a function of the laser energy or the ion-impact energy researchers will extract valuable information about the system. Furthermore, the time of flight of the electrons from the irradiated target to the detector will be computed and the variation in this flight-time as a function of laser frequency will enable further insights into the scientific processes. Following the impact of positrons, the formation of the positronium (Ps) is a vital process in nature, although no attempt of Ps formation using gas-phase fullerene systems has been made until recent research that came from this program. The science to be learned from the study of Ps formation should be universal for Ps formation from nanosystems ushering new directions of Ps spectroscopy. In general, results are expected to motivate experiments and induce collaborations with experimental groups. Students and postdoctoral researchers will be involved for excellent experience in education and opportunities to become expert researchers.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.