Conformer-specific Infrared spectroscopy of cationic Criegee intermediates syn- and anti-CH<sub>3</sub>CHOO<sup></sup>.

Huang, Ende; Zhong, Licheng; Xue, Jingning; Zhou, Xiaohu; Liu, Siyue; Che, Li; Li, Hongwei; Fan, Hongjun et al. · Nat Commun · 2025

basic_science · Level V

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Abstract

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-CH<sub>3</sub>CHOO<sup>+</sup>, 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 CH<sub>3</sub>CHOO, 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.