RUI: Negative Ion Spectroscopy and Dynamics

The primary goal of this project is to improve the understanding of how electrons interact with each other on the atomic scale, which is crucial for the stability of atoms and for the formation of molecules through chemical reactions. To gain insights into electron interactions, the faculty and undergraduate student researchers will experimentally investigate the properties of negative ions (atoms with an extra electron).

Negative ions are important in a wide variety of physical situations ranging from electrical sparks to the atmospheres of planets and stars. In experiments at Denison University (an undergraduate institution) and at a national lab facility in Sweden, laser light will be used to excite or detach electrons from negative ions; the laser supplies a finely controlled amount of input energy to probe interactions within the ions.

The results will build the fundamental atomic physics database, provide valuable tests of state-of-the-art theoretical atomic structure calculations, and yield key insights into dynamical many-body interactions, which is a topic of interest for a broad range of fields in physics, chemistry, materials science, and nanotechnology. Students will participate in all aspects of the research, providing significant technical training for young scientists in cutting-edge electronics, lasers, and computers, and enhancing their ability for future careers in science, technology, and engineering.

The interactions of photons with negative ions will be investigated in two series of photoexcitation and photodetachment 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 detailed atomic physics calculations regarding these multi-body interactions.

Planned studies of the negative ion of thorium are particularly important because it is a promising candidate for laser cooling, which has not yet been achieved with negative ions but could potentially open up the ultracold regime for a wide range of negatively-charged species through sympathetic collisional cooling. On-campus at Denison University, the faculty and student researchers will use an ion beam–tunable infrared laser system to measure multiple bound states of the thorium anion with resonant two-photon detachment spectroscopy.

They will also use photodetachment threshold spectroscopy to measure the isotope shift in the electron affinity of thallium, which is sensitive to interactions of electrons both with each other and with the nucleus. Complementary experiments of excited state lifetimes, decay processes, and isotope shifts in negative ions will be performed at Stockholm University in Sweden using the cryogenic electrostatic ion storage ring DESIREE.

The dynamic multi-electron interactions in highly-correlated negative ions continue to challenge the fundamental understanding of atomic structure, and this project will extend the available experimental data to more complex negative ion systems, spur new theoretical studies, and directly address pressing open questions in the field. Support from this grant will enhance the research and teaching infrastructure of Denison University and provide undergraduate students valuable research experiences and technical training which will prepare them for advanced study and STEM careers.

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.