JILA Thesis Defense - Ya-Chu Chan

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Title: High-Resolution Infrared Spectroscopy of Cold Molecules: From Small Radicals and Ions to Large Fullerenes

Speaker: Ya-Chu Chan

Event Details / Abstract: Spectroscopy provides a powerful tool for probing molecular structure and dynamics, but extending high-resolution measurements to increasingly complex molecules presents significant challenges. Dense rotational structures, spectral fragmentation arising from intramolecular vibrational redistribution, and low-frequency, large-amplitude molecular motions can lead to severe spectral congestion, making individual transitions difficult to resolve. In this talk, I will discuss how combining sensitive infrared absorption spectroscopy with molecular cooling techniques enables detailed studies of molecules ranging from small reactive radicals to large fullerenes. High-resolution spectroscopy of bromomethylene radical (CHBr) reveals vibrationally induced charge redistribution, nuclear quadrupole hyperfine interactions, and non-equilibrium vibrational relaxation. For fullerenes, cryogenic buffer-gas cooling enables direct observation of nuclear-spin statistical effects in C₆₀ and the first rotationally resolved infrared spectrum of C₇₀. Finally, I will present recent progress toward higher spectral resolution using an extracted C₆₀ molecular beam. Together, these results demonstrate new opportunities for precision spectroscopy of increasingly complex molecules.