OH Roaming and Beyond in the Unimolecular Decay of the Methyl-Ethyl-Substituted Criegee Intermediate: Observations and Predictions
Abstract
Alkene ozonolysis generates short-lived Criegee intermediates that are a significant source of hydroxyl (OH) radicals. This study demonstrates that roaming of the separating OH radicals can yield alternate hydroxycarbonyl products, thereby reducing the OH yield. Specifically, hydroxybutanone has been detected as a stable product arising from roaming in the unimolecular decay of the methyl-ethyl-substituted Criegee intermediate (MECI) under thermal flow cell conditions. The dynamical features of this novel multistage dissociation plus a roaming unimolecular decay process have also been examined with ab initio kinetics calculations. Experimentally, hydroxybutanone isomers are distinguished from the isomeric MECI by their higher ionization threshold and distinctive photoionization spectra. Moreover, the exponential rise of the hydroxybutanone kinetic time profile matches that for the unimolecular decay of MECI. A weaker methyl vinyl ketone (MVK) photoionization signal is also attributed to OH roaming. Complementary multireference electronic structure calculations have been utilized to map the unimolecular decay pathways for MECI, starting with 1,4 H atom transfer from a methyl or methylene group to the terminal oxygen, followed by roaming of the separating OH and butanonyl radicals in the long-range region of the potential. Roaming via reorientation and the addition of OH to the vinyl group of butanonyl is shown to yield hydroxybutanone, and subsequent C–O elongation and H-transfer can lead to MVK. A comprehensive theoretical kinetic analysis has been conducted to evaluate rate constants and branching yields (ca. 10–11%) for thermal unimolecular decay of MECI to conventional and roaming products under laboratory and atmospheric conditions, consistent with the estimated experimental yield (ca. 7%).
Copyright and License
© 2023 American Chemical Society.
Acknowledgement
Research at the University of Pennsylvania is supported by the National Science Foundation under grants CHE-1955068 and CHE-2301298 with partial equipment support from the U.S. Department of Energy–Basic Energy Sciences under grant DE-FG02-87ER13792. This work utilized the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the National Science Foundation grant number ACI-1548562 through the allocation TG-CHE190088. C.A.S. acknowledges support from NSF CHE-2102626. Argonne National Laboratory is supported by the USDOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences, under Contract No. DE-AC02-06CH11357. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the USDOE's National Nuclear Security Administration under contract DE-NA0003525. The operation of the multiplexed photoionization mass spectrometry kinetics experiments and the participation of the Sandia personnel were supported by Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, of the U.S. Department of Energy. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the USDOE or the U.S. Government. T.L. and M.I.L. thank Penn undergraduate Khaliun Dorjmenchim for making the videos. C.R.M. is grateful for support from an A. O. Beckman postdoctoral fellowship. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). Financial at JPL support was provided by the NASA Upper Atmosphere Research and the Tropospheric Composition programs.
Data Availability
All data are available in the main text, Supporting Information, and Zenodo, (56) the latter of which contains the input file for the Master Equation System Solver (MESS).
Conflict of Interest
The authors declare no competing financial interest.
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ja3c07126_si_001.pdf
Additional details
Identifiers
- ISSN
- 1520-5126
Related works
- Is supplemented by
- Software: https://zenodo.org/record/8278358 (URL)
Funding
- National Science Foundation
- CHE-1955068
- National Science Foundation
- CHE-2301298
- United States Department of Energy
- DE-FG02-87ER13792
- National Science Foundation
- ACI-1548562
- National Science Foundation
- TG-CHE190088
- National Science Foundation
- CHE-2102626
- United States Department of Energy
- DE-AC02-06CH11357
- National Nuclear Security Administration
- DE-NA0003525
- United States Department of Energy
- DE-AC02-05CH11231
- Arnold and Mabel Beckman Foundation
- National Aeronautics and Space Administration