Unimolecular chemistry of neutrals and cations by photoelectron photoion coincidence spectroscopy Andras Bodi 1 , Patrick Hemberger 1 , Bálint Sztáray 2 , Jordy Bouwman 3 and Xiangkun Wu 1 1 Paul Scherrer Institute, Switzerland, 2 University of the Pacific, United States, 3 University of Colorado, United States Threshold photoionization has been established as a versatile tool to understand the unimolecular fragmentation of internal energy selected ions 1 as well as a universal, sensitive and specific tool to detect elusive intermediates in gaseous reactive environments. 2, 3 Here, we review how PEPICO detection and statistical modeling revealed six fragmentation channels leading to only three fragment ion mass channels and their kinetics in the 1,3-dioxolane cation. 4 Neutral detection can also offer insights into competing reaction steps. For instance, several product channels are energetically allowed in the barrierless association reaction of benzyne + allyl. The observed branching ratios of the intermediate, derived based on photoion mass-selected threshold photoelectron spectra, as well as the unimolecular stabilization of various isomerization products by hydrogen atom loss, observed in a flash vacuum pyrolysis experiment, can be understood in terms of the reactor environment and unimolecular kinetics. 5 Detection minutiae in probing pyrolysis experiments, such as sampling effects and temperatures, will also be addressed. 6 References 1. T. Baer and R. P. Tuckett, Phys Chem Chem Phys , 2017, 19 , 9698-9723. 2. P. Hemberger, J. A. van Bokhoven, J. Pérez-Ramírez and A. Bodi, Catal Sci Technol , 2020, 10 , 1975-1990. 3. P. Hemberger, A. Bodi, T. Bierkandt, M. Köhler, D. Kaczmarek and T. Kasper, Energy Fuels , 2021, 35 , 16265-16302. 4. P. Weidner, K. Voronova, A. Bodi and B. Sztaray, J. Mass Spectrom. , 2020, 55 , e4522. 5. M. N. McCabe, P. Hemberger, E. Reusch, A. Bodi and J. Bouwman, J Phys Chem Lett , 2020, 11 , 2859-2863. 6. P. Hemberger, X. Wu, Z. Pan and A. Bodi, J Phys Chem A , 2022, DOI: 10.1021/acs.jpca.2c00766
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