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Title: Experimental and theoretical studies of the doubly substituted methyl-ethyl Criegee intermediate: Infrared action spectroscopy and unimolecular decay to OH radical products

Abstract

In this work the infrared (IR) action spectrum of the doubly substituted methyl-ethyl Criegee intermediate (MECI) is observed in the CH stretch overtone region with detection of OH products. The MECI exhibits four conformers, all of which undergo unimolecular decay via a 1,4 H-atom transfer mechanism, followed by the rapid release of OH products. Conformers with different orientations of the carbonyl oxide group with respect to the methyl and ethyl substituents (i.e., anti and syn) decay via distinct transition state barriers (16.1 kcal mol–1 and 15.4 kcal mol–1, respectively). The observed IR action spectrum is in good agreement with the predicted anharmonic IR absorption spectrum, but exhibits significant congestion, which is attributed to couplings between spectroscopic bright states and nearby dark states. Energy-dependent OH appearance rates are measured upon IR excitation of the strongest features in the IR action spectrum and are found to be on the order of 106–107 s–1. The experimental rates are in good agreement with computed Rice–Ramsperger–Kassel–Marcus rates for the unimolecular decay of MECI at these energies, which incorporate quantum mechanical tunneling and sophisticated hindered rotor treatments, as well as high-level theoretical calculations of the TS barrier heights, rovibrational properties, and torsional barriers associated with themore » MECI conformers. Master equation modeling is used to predict thermal rates for the unimolecular decay of anti- and syn-MECI of 473 s–1 and 660 s–1, respectively. Comparison with other previously studied Criegee intermediate systems provides insights into substituent effects on unimolecular decay under both energy-dependent and thermal conditions.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [3]; ORCiD logo [2]
  1. Univ. of Pennsylvania, Philadelphia, PA (United States)
  2. Univ. of Pennsylvania, Philadelphia, PA (United States
  3. Argonne National Lab. (ANL), Lemont, IL (United States)
Publication Date:
Research Org.:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Org.:
National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; Carlsberg Foundation; Independent Research Fund Denmark; Julie von Müllens Fond
OSTI Identifier:
1632301
Alternate Identifier(s):
OSTI ID: 1602341
Grant/Contract Number:  
AC02-06CH11357; CHE-1664572; ACI-1548562; CF18-0614; 9036-00016B
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 152; Journal Issue: 9; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Action spectroscopy; Atom transfer reactions; Free radicals; Ozonolysis; Quantum tunneling; Transition state

Citation Formats

Barber, Victoria P., Hansen, Anne S., Georgievskii, Yuri, Klippenstein, Stephen J., and Lester, Marsha I. Experimental and theoretical studies of the doubly substituted methyl-ethyl Criegee intermediate: Infrared action spectroscopy and unimolecular decay to OH radical products. United States: N. p., 2020. Web. doi:10.1063/5.0002422.
Barber, Victoria P., Hansen, Anne S., Georgievskii, Yuri, Klippenstein, Stephen J., & Lester, Marsha I. Experimental and theoretical studies of the doubly substituted methyl-ethyl Criegee intermediate: Infrared action spectroscopy and unimolecular decay to OH radical products. United States. https://doi.org/10.1063/5.0002422
Barber, Victoria P., Hansen, Anne S., Georgievskii, Yuri, Klippenstein, Stephen J., and Lester, Marsha I. Mon . "Experimental and theoretical studies of the doubly substituted methyl-ethyl Criegee intermediate: Infrared action spectroscopy and unimolecular decay to OH radical products". United States. https://doi.org/10.1063/5.0002422. https://www.osti.gov/servlets/purl/1632301.
@article{osti_1632301,
title = {Experimental and theoretical studies of the doubly substituted methyl-ethyl Criegee intermediate: Infrared action spectroscopy and unimolecular decay to OH radical products},
author = {Barber, Victoria P. and Hansen, Anne S. and Georgievskii, Yuri and Klippenstein, Stephen J. and Lester, Marsha I.},
abstractNote = {In this work the infrared (IR) action spectrum of the doubly substituted methyl-ethyl Criegee intermediate (MECI) is observed in the CH stretch overtone region with detection of OH products. The MECI exhibits four conformers, all of which undergo unimolecular decay via a 1,4 H-atom transfer mechanism, followed by the rapid release of OH products. Conformers with different orientations of the carbonyl oxide group with respect to the methyl and ethyl substituents (i.e., anti and syn) decay via distinct transition state barriers (16.1 kcal mol–1 and 15.4 kcal mol–1, respectively). The observed IR action spectrum is in good agreement with the predicted anharmonic IR absorption spectrum, but exhibits significant congestion, which is attributed to couplings between spectroscopic bright states and nearby dark states. Energy-dependent OH appearance rates are measured upon IR excitation of the strongest features in the IR action spectrum and are found to be on the order of 106–107 s–1. The experimental rates are in good agreement with computed Rice–Ramsperger–Kassel–Marcus rates for the unimolecular decay of MECI at these energies, which incorporate quantum mechanical tunneling and sophisticated hindered rotor treatments, as well as high-level theoretical calculations of the TS barrier heights, rovibrational properties, and torsional barriers associated with the MECI conformers. Master equation modeling is used to predict thermal rates for the unimolecular decay of anti- and syn-MECI of 473 s–1 and 660 s–1, respectively. Comparison with other previously studied Criegee intermediate systems provides insights into substituent effects on unimolecular decay under both energy-dependent and thermal conditions.},
doi = {10.1063/5.0002422},
journal = {Journal of Chemical Physics},
number = 9,
volume = 152,
place = {United States},
year = {Mon Mar 02 00:00:00 EST 2020},
month = {Mon Mar 02 00:00:00 EST 2020}
}

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