Abstract:
Detecting and quantifying hydrocarbon radicals in reactive environments and mixtures is critical to understanding the formation and fate of complex organic molecules both on Earth and in space. Microwave spectroscopy is an ideal tool for this specific application because the unique rotational fingerprints of molecules are isomer, isotopic and internal quantum state specific. A prominent barrier to widely applying these tools to chemical analysis, however, is the extensive fine and hyperfine structure intrinsic to open-shell hydrocarbons that arises from the interaction of their unpaired electronic spins with orbital angular momentum, total molecular rotation, and nuclear spins, which is readily observed at high spectral resolution. The latter interactions are especially problematic as the corresponding spectral splittings and congestion scale exponentially with the number of nuclear spins (e.g., H or 13C)—in many cases precluding a complete spectroscopic analysis of the necessary accuracy for robust and quantitative characterization. This talk will highlight the comprehensive and exhaustive analysis of the hyperfine-resolved microwave spectra of radical intermediates with multiple nuclear spins, including phenyl, propargyl, and cyclopropyl. The highly precise spectroscopic parameters derived from this work provide insights as to the electronic structure and interactions of these fundamental π- and σ-radicals. The precise rest frequencies calculated from these constants enable new investigations of their chemistry in diverse laboratory, terrestrial, and astronomical environments. A similar approach is likely to succeed when applied to other large, open-shell hydrocarbons and metal-ligand complexes, laying the foundation to exploit state-of-the-art microwave techniques to yield new insights into crucial reactive organic and inorganic species.
Bio:
Bryan Changala received a B.S. in Chemistry and Physics from the Massachusetts Institute of Technology in 2013. He completed his Ph.D. in Physics in 2019 in the Ye group at JILA, University of Colorado Boulder, where he applied infrared frequency combs to the spectroscopy of buckminsterfullerene and other complex polyatomic molecules. From 2020 to 2024, he was a postdoctoral fellow in the McCarthy laboratory at the Center for Astrophysics | Harvard & Smithsonian. Bryan returned to CU as an Associate JILA Fellow and Asst. Professor of Physics, Adjoint, in January 2025. His research group develops optical frequency comb and microwave spectroscopy techniques in tandem with sophisticated quantum chemical methods to address a wide range of topics in chemical physics, astrochemistry, and fundamental quantum molecular science.
The Physics Frontiers Centers (PFC) program supports university-based centers and institutes where the collective efforts of a larger group of individuals can enable transformational advances in the most promising research areas. The program is designed to foster major breakthroughs at the intellectual frontiers of physics by providing needed resources such as combinations of talents, skills, disciplines, and/or specialized infrastructure, not usually available to individual investigators or small groups, in an environment in which the collective efforts of the larger group can be shown to be seminal to promoting significant progress in the science and the education of students. PFCs also include creative, substantive activities aimed at enhancing education, broadening participation of traditionally underrepresented groups, and outreach to the scientific community and general public.