Seeing the Unseen: Detection of Reactive Intermediates with VUV Sychrotron Radiation

Chemical reactions are controlled by species we rarely detect: e.g. short-lived carbenes, radicals, and ketenes steer reaction pathways and ultimately determine selectivity and yield. Conventional tools such as GC/MS or NMR usually miss intermediates, even though mechanistic insight is urgently needed for rational process optimization.

In this talk, I introduce Photoelectron Photoion Coincidence (PEPICO) spectroscopy with vacuum ultraviolet (VUV) synchrotron radiation at the Swiss Light Source as a multiplexed approach to reaction analysis. By detecting both ions and electrons after VUV ionization, PEPICO connects mass spectrometry with isomer-selective photoelectron fingerprints, allowing us to disentangle complex reaction mixtures.

We will illustrate how this approach changes our mechanistic understanding in heterogeneous catalysis and high-temperature chemistry, including zeolite-catalyzed plastic pyrolysis, where we identify mechanistic routes to benzene, toluene, and xylenes. Moreover, we turn to biomass conversion, where transient ketenes are the unwelcome guests that steer selectivity off-target.

I will leave you with a practical sense of what intermediates we can observe, how spectra are interpreted, and where PEPICO detection can unveil new mechanistic insights.