Electronic Spectroscopy and Characterization of the Singly Fluorinated Criegee Intermediate FCHOO

The fluorinated Criegee intermediate, FCHOO, is produced from the ozonolysis of hydrofluoroolefins (HFOs), which are next-generation refrigerants. FCHOO was laboratory-generated for the first time from a diiodo precursor and examined using both spectroscopic and theoretical methods. Specifically, FCHOO is detected by VUV photoionization at 118 nm and spectroscopically characterized via ultraviolet-visible (UV-vis)-induced depletion of the parent mass (m/z = 64) under jet-cooled conditions. A broad experimental absorption spectrum resulting from a strong π* ← π transition spans from 280 to 430 nm and peaks at 338 nm. Multireference electronic structure calculations are carried out to explore the impact of the fluorine substituent on the ground- and excited-state electronic structures. The vertical excitation energies of syn- and anti-FCHOO differ considerably (318 and 371 nm, respectively), and both are shifted compared to CH₂OO (328 nm). Spectral simulations using a nuclear ensemble method indicate similar contributions to the experimental spectrum from the syn and anti conformers of FCHOO, which are predicted to have comparable ground-state stabilities. Natural bond orbital analysis highlights the nonbonding interactions in the ground state that give rise to the slight energetic splitting between the two conformers.