RUI: Negative Ion Photodetachment Spectroscopy and Lifetimes

General audience abstract:

This project will experimentally investigate the properties of negative ions, which are atoms or molecules with an extra electron. Negative ions are important in a variety of physical situations including chemical reactions, the atmospheres of planets and stars, and electrical plasmas. The primary goal of the project is to improve the understanding of how electrons interact with each other on the atomic scale (“electron correlation”) — a very important aspect of quantum mechanics that plays a key role in the structure of atoms and molecules.

In experiments at Denison University and at the DESIREE 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 electron correlations within the ions. The results will build the fundamental physical chemistry database, provide valuable tests of state-of-the-art theoretical atomic structure calculations, and yield key insights into dynamical many-body interaction, which is a topic of interest for a broad range of fields in physics, chemistry, materials science, and nanotechnology.

Undergraduate 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 advanced study and future careers in science, technology, and engineering. Technical audience abstract:

The interactions of photons with negative ions will be investigated in a series 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.

An ion beam–tunable infrared laser system at Denison University will be used to measure multiple bound states of the negative ion of thorium with resonant two-photon detachment spectroscopy. Complementary experiments of excited state lifetimes and decay processes in the negative ion of lanthanum will be performed at Stockholm University in Sweden using the cryogenic electrostatic ion storage ring DESIREE.

Thorium and lanthanum are important to investigate because they are promising candidates 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. The faculty and student researchers will also use photodetachment threshold spectroscopy to measure isotope shifts in the electron affinities of lead and thallium, which are sensitive to interactions of electrons both with each other and with the nucleus.

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 (an undergraduate college) and provide students with valuable experimental research experiences and technical training.

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.