Mass-Resolved Isomer-Selective Chemical Analysis with Imaging Photoelectron Photoion Coincidence Spectroscopy

Photoionization mass spectrometry is a powerful method for time- and space-resolved chemical analysis of reactants, intermediates, and products. Tunable synchrotron light enables isomer separation based on unique photoionization spectra; however, mixtures of three or more isomers can be difficult to resolve by this method. In this work we demonstrate, by measuring the photoelectron spectrum corresponding to each cation m/z ratio, that imaging photoelectron photoion coincidence spectroscopy provides a more detailed spectral fingerprint than photoionization spectra. This method offers increased selectivity for analyzing gas-phase mixtures of many components. Mixtures of C4H6 and four C5H8 unsaturated hydrocarbons were analyzed, and the components could easily be identified based On mass selected threshold photoelectron spectra (scanning the photon energy) or photoelectron velocity map images (PEVMIs) at a single or a few fixed photon energies. The PEVMI approach is more highly multiplexed, trading somewhat lower spectral resolution for faster data acquisition and photoelectron angular distributions.