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Electronic Spectroscopy and Characterization of the Singly Fluorinated Criegee Intermediate FCHOO
Elizabeth Karlsson1, Rawan Rabayah1, Tolga N V Karsili2
1Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States.
The Journal of Physical Chemistry. A
|August 29, 2025
Summary
The first laboratory generation of fluorinated Criegee intermediate (FCHOO) from hydrofluoroolefins (HFOs) was achieved. Spectroscopic and theoretical methods characterized FCHOO, revealing its absorption spectrum and conformer properties.
Area of Science:
- Atmospheric Chemistry
- Physical Chemistry
- Spectroscopy
Background:
- Hydrofluoroolefins (HFOs) are next-generation refrigerants.
- Criegee intermediates play a crucial role in atmospheric chemistry.
- The properties of fluorinated Criegee intermediates are not well understood.
Purpose of the Study:
- To synthesize and characterize the fluorinated Criegee intermediate (FCHOO) in the laboratory.
- To investigate the impact of fluorine substitution on the electronic structure and spectroscopy of Criegee intermediates.
- To compare the properties of FCHOO with non-fluorinated analogs.
Main Methods:
- Laboratory generation of FCHOO from a diiodo precursor.
- Detection using vacuum ultraviolet (VUV) photoionization at 118 nm.
- Spectroscopic characterization via UV-vis-induced depletion spectroscopy under jet-cooled conditions.
- Multireference electronic structure calculations.
- Nuclear ensemble method for spectral simulations.
- Natural bond orbital (NBO) analysis.
Main Results:
- FCHOO was successfully generated and detected.
- An experimental absorption spectrum was obtained, spanning 280-430 nm with a peak at 338 nm, attributed to a π* ← π transition.
- Theoretical calculations predicted distinct vertical excitation energies for syn- (318 nm) and anti- (371 nm) FCHOO conformers.
- Spectral simulations indicated comparable contributions from both syn and anti conformers to the experimental spectrum.
- Ground-state stabilities of the syn and anti conformers were predicted to be similar, with slight energetic splitting due to nonbonding interactions.
Conclusions:
- The study provides the first laboratory characterization of FCHOO.
- The fluorine substituent significantly influences the electronic structure and spectral properties of Criegee intermediates.
- Both syn and anti conformers of FCHOO contribute to the observed spectrum and possess comparable stability.
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