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 state photodetachment thresholds of several lanthanide and Group III negative ions will be measured in order to determine the atomic electron affinities. 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 appear to exist in the negative ions of Ce and La. The second series of complementary experiments will investigate inner-shell photodetachment from the negative ions of oxygen, C60 and other atomic and molecular species using high energy photons at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. These experiments continue a series of studies by the PIs to investigate 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.
The broader impacts of the program include contributions to the database of atomic properties, connections to other scientific fields, and the education of undergraduate students. The high-precision electron affinities measured in this project will be useful for modeling of chemical reactions and plasma interactions for such practical applications as semiconductor processing. The detailed studies of negative ions will yield insights into dynamical many-body interaction, which is a 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 ALS, providing important research experiences for young scientists including technical training in electronics, computers, lasers, and optics. Additionally, both PIs and many of our Undergraduate students are also heavily involved with student-faculty collaborative public science outreach projects that present Physics and Astronomy programs to hundreds of people each year.
