Our group uses synchrotron-based photoionization mass spectrometry to directly observe and characterize transient chemical intermediates in reactive systems. These experiments allow us to disentangle complex photodissociation and reaction pathways, quantify product branching ratios, and identify short-lived species that are often inaccessible using conventional spectroscopic techniques.
We conduct these experiments at the Chemical Dynamics Beamline of the Advanced Light Source, a U.S. Department of Energy user facility. The instrument we use—the multiplexed photoionization mass spectrometer (MPIMS)—was developed by our close collaborator Dr. David Osborn (Sandia National Laboratories). While the instrumentation is well established, the chemical design, kinetic modeling, and interpretation of each experiment are driven entirely by our research team.
Figure 1. The group at the Chemical Dynamics Beamline in 2022 with David Osborn.
Our first major publication using this platform was the direct gas-phase detection of singlet carbene HCOH, produced via 193 nm photodissociation of methanol. Using tunable vacuum ultraviolet (VUV) light and time-resolved mass spectrometry, we were able to distinguish HCOH from its structural isomer formaldehyde (H2CO), based on both photoionization energy and decay kinetics.
Figure 2. Photon energy-resolved photoionization signal of HCOH formed from CH3OH photodissociation, extracted observation of m/z = 30 at low energies.
Beyond detection, a major component of our group’s contribution lies in building and validating detailed chemical models. These experiments often require us to construct multi-generational, 200+ reaction kinetic networks that account for primary photodissociation, secondary radical chemistry, and isomerization. Our team leads the effort to fit these models to the experimental data and extract mechanistic insight from overlapping signals and competing channels.
Ongoing work builds on this platform to quantify branching ratios in competitive photodissociation pathways.
Selected Publication
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Hockey, E. K., et al. “Direct observation of gas-phase hydroxymethylene: Photoionization and kinetics resulting from methanol photodissociation,”
J. Am. Chem. Soc., 2024, 146, 14416–14421.
DOI: 10.1021/jacs.4c03090