RUI: The Interaction of Radiation with Free and Confined Quantum Systems

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The response of a physical system to incoming electromagnetic radiation or charged particles is one of the most basic properties of nature of utter importance to both fundamental and applied sciences along with a wide variety of technological applications. Despite numerous studies of these processes performed to date, the current understanding of them is far from complete. This is because the processes are multifaceted in the richness of phenomena that might occur, and are extremely difficult for theory to embrace all of them, or even some of them. In this project, the understanding of the structure and spectra of free and confined atoms and their interactions with incoming electromagnetic radiation or charged particles will be advanced. In the project, confined atoms of interest are defined as atoms which are embedded into hollow interiors of various gas-phase fullerenes Cn or other types of penetrable and impenetrable confinements with varying heights and widths, as well as positioned near planar or non-planar graphitic nano-structures. New trends in the cross sections of corresponding processes of photon absorption and collision of the incoming electrons with confined and free atoms will be unveiled. For free atoms, this will be achieved by accounting for the interactions mixing a 'pure' vacancy state (such, e.g., as 5s in Ba) or 'pure' incoming particle state with dominant (to be determined in the project) higher order continuous state excitations in a number of atoms, in the first hand in Ba and Mn; so far, the needed understanding is lacking. For confined atoms, new trends in their spectra will be unraveled by accounting for individual and combined effects brought about by the above specified confinements of different properties and geometry, by varying positions of the confined atom inside a confinement, and by accounting for multielectron interactions (electron correlation) in the atom itself. Hartree-Fock approximation, random phase approximation with exchange, methods of many-body perturbation theory, etc., will be employed in, or adjusted to, the stated studies. The intellectual merit of activities to be performed is determined by the fact that to date there is little knowledge on how the individual and combined effects of nano-scaled confinements of different symmetries (spherical, non-spherical, homogeneous, inhomogeneous, planar, non-planar, etc.) may alter the structure and spectra of confined in, or positioned near them atoms. Also, to date, there remains a lack of understanding of the interactions mixing pure vacancy/particle states in an atom with its higher order excitations. Moreover, results of the project will identify some of the most interesting and/or useful future measurements/calculations which could be performed, both for free and confined atoms, thereby contributing synergy to advancement of the field. On a broader impact scale, the involvement and active participation of undergraduate students in this project will strengthen integration of research and education at the University. Furthermore, the project will enhance the research infrastructure in the University. Results of research will be disseminated broadly to scientific community and general public for a broader awareness of science. Society will benefit from the performed activities by gaining new fundamental knowledge on phenomena of nature with important applications, and by the training of students who, early in their careers, will have acquired a unique professional experience for entry into graduate study in physics or scientific and engineering careers. All of the above will significantly contribute to the benefit, health, vitality of science and engineering, and the prosperity of society.