Chemistry Cheminar - Professor Jinjun Liu; University of Louisville, Department of Chemistry

Seminar Title: High-resolution spectroscopy of open-shell molecules in nearly degenerate states

Jinjun Liu, Department of Chemistry, University of Louisville, Louisville, KY, USA.

Rovibronic (rotational-vibrational-electronic) structure of molecules in orbitally degenerate electronic states, including Renner-Teller (RT) and Jahn-Teller (JT) active molecules, has been extensively studied.[1-3] Less is known about the rotational and fine structure of polyatomic molecules in nearly degenerate states, especially those with low (e.g., Cs or C1) symmetry that are subject to the pseudo-Jahn-Teller (pJT) effect.[4] In the case of free radicals, the unpaired electron further complicates energy levels by inducing spin-orbit (SO) and spin-rotation (SR) splittings. State-coupling also affects the intensities of rotational and vibronic transitions. New spectroscopic models are required to reproduce the spin-rovibronic structure and simulate the experimentally obtained spectra of JT- and pJT-active free radicals.[5-7] The study on free radicals in nearly degenerate states provides a promising avenue of research, which bridges the gap between symmetry-induced degenerate states and the Born-Oppenheimer (BO) limit of unperturbed electronic states. In this talk, I will explain the sophisticated intramolecular interactions using cartoon animations and terminology that is familiar to senior undergraduate students and first-year master students. I will try to prove that rotational and fine-structure analysis of spectra involving nearly degenerate states can aid in vibronic analysis and interpretation of effective molecular constants. If time permits, I will briefly discuss the implications of the present research on laser cooling of polyatomic molecules.

[1] “The Renner–Teller effect revisited 40 years later”, C. Jungen, J. Mol. Spectrosc. 363, 111172 (2019).
[2] ``Quantitative insights about molecules exhibiting Jahn-Teller and related effects,'' T. Barckholtz and T. A. Miller, Int'l. Rev. of Phys. Chem. 17, 435 (1998).
[3] "Vibronically coupled states: Computational considerations and characterization of vibronic and rovibronic spectroscopic parameters," K. Sharma, T. A. Miller, and J. F. Stanton Int'l. Rev. Phys. Chem. 40, 165 (2021).
[4] "Electronic spectroscopy of the ~????12A"/~????22A'-~????2A' transitions of jet-cooled calcium ethoxide radicals: Vibronic structure of alkaline earth monoalkoxide radicals of Cs symmetry", A. C. Paul, K. Sharma, H. Telfah, T. A. Miller, and J. Liu, J. Chem. Phys. 155, 024301 (2021).
[5] “Rotationally resolved ~B-~X electronic spectra of the isopropoxy radical: A comparative study”, J. Liu, D. Melnik, and T. A. Miller, J. Chem. Phys. 139, 094308 (2013)
[6] “Jet-cooled laser-induced fluorescence spectroscopy of cyclohexoxy: Rotational and fine structure of molecules in nearly degenerate electronic states”, J. Liu and T. A. Miller, J. Phys. Chem. A 118, 11871 (2014).
[7] “Rotational and fine structure of open-shell molecules in nearly degenerate electronic states”, J. Liu, J. Chem. Phys. 148, 124112 (2018).

Bio:
Dr. Jinjun Liu is an Associate Professor of Chemistry and an Adjunct Professor of Physics at the University of Louisville. He received his B.S. degree in physics at East China Normal University in 1999 and worked for two years in the State Key Laboratory of Precision Spectroscopy in Shanghai. For his Ph.D., he studied Chemical Physics at the Ohio State University in Dr. Terry A. Miller's research group. Jinjun received his Ph.D. degree in 2007 and served as a post-doctoral fellow with Dr. Frederic Merkt at the Swiss Federal Institute of Technology (ETH), Zurich. He joined the Department of Chemistry at the University of Louisville as an Assistant Professor in January 2012. He was promoted to Associate Professor in 2017. He is also the Spectroscopy Theme Leader at the Conn Center for Renewable Energy Research.