University of Louisville Laser Lab (UL3)

About

Research in the Liu Group at the University of Louisville (UofL) consists of spectroscopic studies on small (but not simple!) molecules using high-resolution laser systems. Our high-resolution laser-spectroscopy studies center on the detection and characterization of reactive chemical intermediates, e.g., free radicals and molecules in excited electronic states. The spectroscopic techniques employed in our experiments include laser-induced fluorescence / dispersed fluorescence (LIF/DF) and cavity ring-down (CRD) spectroscopy. We are also developing a novel cavity-enhanced two-photon double-resonance spectroscopy technique with our state-of-the-art laser systems to study molecular dark states. These studies lead to a quantitative understanding of molecular structure and dynamics and the nature of chemical bonding. Unambiguous identification and analysis of the experimentally obtained spectra is a prerequisite to subsequent work on the chemical reactions that involve chemical reaction intermediates. Recently, we have investigated metal-containing molecules that are promising candidates for direct laser cooling and the search for new physics. We are particularly interested in molecular species with the Jahn-Teller (JT) effect and the pseudo-Jahn-Teller (pJT) effect, vibronic (vibrational-electronic) interactions that cause spontaneous distortion of the symmetry of polyatomic molecules. Our group also develops spectroscopic models to analyze the rotational and fine structure of open-shell molecules (free radicals) in degenerate and nearly degenerate states subject to JT, pJT and spin-orbit (SO) interactions. Quantum chemistry calculations using the density functional theory (DFT), complete active space self-consistent field (CASSCF) and coupled-cluster (CC) methods are used to help understand the energy level structure of molecules and to predict and simulate experimentally obtained spectra. 

Our Work

High-resolution laser spectroscopy of metal-containing molecules for direct laser cooling and quantum information science.
High-resolution laser spectroscopy of astrochemical molecules.Stress
Spectroscopic modelling and quantum chemistry calculations of spin-ro-vibronic structure of open-shell molecules.

[Full List of Publications]

“Mid-infrared Doppler-free saturation absorption spectroscopy of the Q branch  of CH4 ν3=1 band using a rapid-scanning continuous-wave optical parametric oscillator”, S. M. S. Riyadh, H. Telfah, I. W. Jones, J. S. Bersson, C-F. Cheng, S-M. Hu, D. B. Foote, and J. Liu*, Opt. Lett. 49, 4230-4233 (2024). DOI: https://doi.org/10.1364/OL.530567.
“Calculated and empirical values of vibronic transition dipole moments of reactive chemical intermediates for determination of concentrations”, I. W. Jones, J. S. Bersson, J. Liu,∗ K. Sharma, O. A. Vasilyev, T. A. Miller,∗ and J. F. Stanton∗, J. Phys. Chem. A.  127, 4670–4681 (2023). DOI: https://doi.org/10.1021/acs.jpca.3c01584
“Fine and hyperfine structure of PbF in the B2Σ+ state studied by laser-induced fluorescence spectroscopy”, C. Zhu, B. Chen, Y. Chen, T. Yang, H. Wang* , J. Yin, and J. Liu, J. Chem. Phys. 157, 084307 (7 pages) (2022). DOI: https://doi.org/10.1063/5.0099716
"Electronic spectroscopy of the ~𝐴12A"/~𝐴22A'-~𝑋2A' 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 (14 pages) (2021). DOI: https://doi.org/10.1063/5.0056550
"Laser-induced fluorescence and dispersed fluorescence spectroscopy of jet-cooled isopentoxy radicals" Md. A. Reza, A. C. Paul, N. Reilly, and J. Liu,* J. Phys. Chem. A 123, 8441-8447 (2019).  DOI: https://doi.org/10.1021/acs.jpca.9b07307
"Room-temperature cavity ring-down spectroscopy of methyl-allyl peroxy radicals”, Md. A. Reza, H. Telfah, R. Xu, and J. Liu,* J. Phys. Chem. A 123, 3510–3517 (2019). DOI: http://doi.org/10.1021/acs.jpca.9b01233

Team

Jinjun Liu, PI

View Research Profile

Md. Touhidul Islam, Graduate Student
Ian W. Jones, Graduate Student
Rajan Lamichhane, Graduate student
Amy Mason, Graduate student.