Marissa Weichman

Molecular quantum dynamics via state resolved spectroscopies

My research to date has focused on elucidating the structure and dynamics of exotic molecules through novel high resolution spectroscopies.

In the first half of my talk, I will discuss my graduate work, where I developed a high energy resolution variant of anion photoelectron spectroscopy and applied it for transition state spectroscopy experiments of the benchmark F + H₂ and F + CH₃OH bimolecular reactions. Photodetachment of a bound anion similar in geometry to a neutral transition state yields a spectrum showing structure characteristic of the reactive surface, including discrete quantum resonances bound or quasibound along the reaction coordinate. High-level quantum dynamical calculations yield excellent agreement with our experimental results, allow assignment of structure, and demonstrate the utility of transition state spectroscopy experiments as standards for ab initio theoretical treatment of increasingly complex reactions.

In the second half of my talk I will discuss my postdoctoral work, where I have harnessed mid-infrared frequency comb spectroscopy for precise interrogation of unprecedentedly large molecular species. Frequency combs are light sources consisting of thousands of evenly spaced, sharp frequency “teeth.” Cavity-enhanced frequency comb spectroscopy (CE-FCS) matches a comb’s evenly spaced spectral structure to the resonant modes of an optical cavity. This method allows for simultaneous detection of absorption signal across the comb spectrum, extremely high frequency resolution, and high sensitivity as the cavity dramatically enhances the interaction length between light and sample. I have combined buffer gas cooling of large molecules with CE-FCS in order to measure the rovibrational structure of buckminsterfullerene (C₆₀), a molecule of great fundamental interest and a longstanding spectroscopic challenge. Our frequency comb measurements represent the first direct probe of the internal structure of C₆₀ at the single quantum state level and establish it as by far the largest molecule for which a state resolved spectrum has been reported.