RUI: Negative Ion Photodetachment Spectroscopy

Denison University, Granville OH

Investigators

Abstract

Non-technical description: Lasers and other light sources will be used to measure the properties of negative ions, which are atoms and molecules that have an extra electron. High-precision measurements of how tightly the extra electron is bound will be useful for modeling chemical reactions and plasma interactions for such practical applications as the manufacturing of semiconductors for computers and other electronic devices. The detailed studies of negative ions will yield insights into "dynamical many-body interactions" which are central to understanding how collections of particles behave differently from what one would expect from the knowledge gained by studying single particles in isolation. These interactions are general phenomenon of interest for a broad range of fields in physics, chemistry, and materials science, including nanotechnology. The project will enhance the research and teaching infrastructure of Denison University, an undergraduate college. Students will participate in the experiments both on-campus and at the Lawrence Berkeley National Laboratory, providing important research experiences for young scientists including technical training in electronics, computers, lasers, and optics. Technical description: This project studies the interactions of photons with negative ions in two related series of experiments. The extra electron in a negative ion is bound predominantly by electron correlation effects and therefore negative ions provide a fertile testing ground for state-of-the-art atomic physics calculations regarding these multi-body interactions. In the first series of experiments, complex atomic negative ions are investigated on-campus at Denison University using tunable infrared laser light to detach outer-shell electrons. The ground and upper state photodetachment thresholds of several lanthanide and Group III negative ions (gallium and possibly thallium) will be measured in order to determine the electron affinities and energy levels. There is currently strong disagreement between theoretical predictions and experimental photoelectron spectroscopy results for these systems. The faculty and student researchers will also investigate resonances and bound excited states in lanthanide ions including bound-bound electric-dipole transitions that exist in the negative ions of cerium and lanthanum. The second series of complementary experiments will investigate inner-shell photodetachment from the negative ions of oxygen, hydrogen, and carbon chains of n numbers of carbon atoms (O-, H-, C_n-) and other atomic and molecular species using high energy (12-1000 eV) photons at the Advanced Light Source synchrotron. These experiments continue the PIs' investigations into the effects of the outer-shell electrons on the detaching inner electron's wavefunction. The dynamic multi-electron interactions in the photoexcitation of the highly correlated cores of negative ions continue to challenge the fundamental understanding of atomic structure. Investigations into heavy negative ions and detection of the neutral decay products will test the latest theories describing inner-shell photodetachment.