Conformer-specific Infrared spectroscopy of cationic Criegee intermediates syn- and anti-CH₃CHOO

Criegee intermediates are pivotal in atmospheric chemistry, yet their cationic forms remain poorly understood. This study presents the infrared spectra of cationic Criegee intermediates, specifically syn- and anti-CH₃CHOO⁺, using vacuum ultraviolet photoionization coupled with IR photon dissociation spectroscopy. Combined with quantum chemistry calculations, we explore conformer-specific infrared spectra and identify distinct unimolecular reaction pathways for each conformer. Our method reveals structural differences between neutral and cationic CH₃CHOO, including a lower isomerization barrier in the cationic form. This approach enables the investigation of conformer-specific IR spectroscopy for cationic species, which is challenging using direct IR absorption methods. By exploiting these distinct reaction pathways, we can conduct conformer-specific spectroscopic studies, advancing our ability to trace specific molecular conformations in complex chemical processes in both atmospheric and interstellar contexts.