Physical Chemistry Seminar: Professor Shaowei Li, University of California, San Diego
About the Seminar
"Infrared Integrated Scanning Tunneling Microscopy: New Opportunity in Single Molecule Chemistry from Space to Time"
Probing molecular vibrations at the single-molecule level is essential for achieving bond-specific chemical control in realistic heterogeneous environments. Here, we introduce infrared-integrated scanning tunneling microscopy (IRiSTM), a new measurement platform that combines frequency-tunable infrared excitation with STM to characterize both vibration-mediated nuclear motion and coherent vibrational dynamics in individual molecules. We first validated IRiSTM by monitoring the infrared-induced rotation of ethynyl radicals and then applied it to map the conformational dynamics of pyrrolidine. The resulting broadband spectra revealed fundamental vibrations together with rich overtone and combination bands that are inaccessible to conventional methods, with spectral assignments confirmed by isotopic substitution. Density functional theory calculations showed that delocalized vibrational modes coupled to pyrrolidine ring puckering drive the structural transition, revealing selection rules distinct from those of conventional infrared spectroscopy. By extending IRiSTM into the time domain, we further resolved the coherent evolution and dephasing of individual vibrational modes, as well as quantum beating between multiple modes within a single molecule. IRiSTM enables the investigation of molecular vibrations, coherence, and structural transformations with atomic-scale precision, opening new opportunities for bond-selective chemistry and molecular-scale quantum control.
About the Speaker
Dr. Shaowei Li received his B.S. from Nankai University in 2010 and his Ph.D. from the University of California, Irvine in 2017. He subsequently worked as a postdoctoral scholar at Northwestern University and later as a Heising-Simons Junior Fellow at the University of California, Berkeley. He joined the Department of Chemistry at the University of California, San Diego in 2021 as an Assistant Professor and was promoted to Associate Professor with tenure in 2026. He also holds the Yinan Wang Memorial Chancellor Endowed Junior Chair at UC San Diego. Shaowei’s group focuses on probing the fundamental properties of low-dimensional systems, including single molecules and layered materials, using scanning tunneling microscopy and spectroscopy. His group further integrates scanning tunneling microscopy with optical spectroscopy to investigate light–matter interactions at the atomic scale.