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Title: Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures

HOCO is an important intermediate in combustion and atmospheric processes because the OH + CO → H + CO 2 reaction represents the final step for the production of CO 2 in hydrocarbon oxidation, and theoretical studies predict that this reaction proceeds via various intermediates, the most important being this radical. Isotopic investigations of trans- and cis-HOCO have been undertaken using Fourier transform microwave spectroscopy and millimeter-wave double resonance techniques in combination with a supersonic molecular beam discharge source to better understand the formation, chemical bonding, and molecular structures of this radical pair. We find that trans-HOCO can be produced almost equally well from either OH + CO or H + CO 2 in our discharge source, but cis-HOCO appears to be roughly two times more abundant when starting from H + CO 2. Using isotopically labelled precursors, the OH + C 18O reaction predominately yields HOC 18O for both isomers, but H 18OCO is observed as well, typically at the level of 10%-20% that of HOC 18O; the opposite propensity is found for the 18OH + CO reaction. DO + C 18O yields similar ratios between DOC 18O and D 18OCO as those found for OH + C 18O,more » suggesting that some fraction of HOCO (or DOCO) may be formed from the back-reaction H + CO 2, which, at the high pressure of our gas expansion, can readily occur. The large 13C Fermi-contact term (a F) for trans- and cis-HO 13CO implicates significant unpaired electronic density in a σ-type orbital at the carbon atom, in good agreement with theoretical predictions. To conclude, by correcting the experimental rotational constants for zero-point vibration motion calculated theoretically using second-order vibrational perturbation theory, precise geometrical structures have been derived for both isomers.« less
Authors:
 [1] ;  [2] ; ORCiD logo [3] ; ORCiD logo [4] ; ORCiD logo [1] ;  [5]
  1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Harvard Univ., Cambridge, MA (United States). School of Engineering and Applied Sciences
  2. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Harvard Univ., Cambridge, MA (United States). School of Engineering and Applied Sciences; Air Force Research Lab. (AFRL), Kirtland AFB, NM (United States). Space Vechicles Directorate
  3. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Harvard Univ., Cambridge, MA (United States). School of Engineering and Applied Sciences; National Radio Astronomy Observatory (NRAO), Charlottesville, VA (United States)
  4. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Harvard Univ., Cambridge, MA (United States). School of Engineering and Applied Sciences; Univ. of California, Davis, CA (United States). Dept. of Chemistry
  5. Univ. of Texas, Austin, TX (United States). Dept. of Chemistry and Biochemistry
Publication Date:
Grant/Contract Number:
FG02-07ER15884; CHE-1012743; F-1283; CHE-1361031
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 144; Journal Issue: 12; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of Texas, Austin, TX (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); Robert A. Welch Foundation
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; combustion; isomerism; atmospheric processes; rotational spectra; organic compounds; chemical compounds and components; chemical bonding; perturbation theory; chemical elements; radio spectrum
OSTI Identifier:
1468981

McCarthy, Michael C., Martinez, Oscar, McGuire, Brett A., Crabtree, Kyle N., Martin-Drumel, Marie-Aline, and Stanton, John F.. Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures. United States: N. p., Web. doi:10.1063/1.4944070.
McCarthy, Michael C., Martinez, Oscar, McGuire, Brett A., Crabtree, Kyle N., Martin-Drumel, Marie-Aline, & Stanton, John F.. Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures. United States. doi:10.1063/1.4944070.
McCarthy, Michael C., Martinez, Oscar, McGuire, Brett A., Crabtree, Kyle N., Martin-Drumel, Marie-Aline, and Stanton, John F.. 2016. "Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures". United States. doi:10.1063/1.4944070. https://www.osti.gov/servlets/purl/1468981.
@article{osti_1468981,
title = {Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures},
author = {McCarthy, Michael C. and Martinez, Oscar and McGuire, Brett A. and Crabtree, Kyle N. and Martin-Drumel, Marie-Aline and Stanton, John F.},
abstractNote = {HOCO is an important intermediate in combustion and atmospheric processes because the OH + CO → H + CO2 reaction represents the final step for the production of CO2 in hydrocarbon oxidation, and theoretical studies predict that this reaction proceeds via various intermediates, the most important being this radical. Isotopic investigations of trans- and cis-HOCO have been undertaken using Fourier transform microwave spectroscopy and millimeter-wave double resonance techniques in combination with a supersonic molecular beam discharge source to better understand the formation, chemical bonding, and molecular structures of this radical pair. We find that trans-HOCO can be produced almost equally well from either OH + CO or H + CO2 in our discharge source, but cis-HOCO appears to be roughly two times more abundant when starting from H + CO2. Using isotopically labelled precursors, the OH + C18O reaction predominately yields HOC18O for both isomers, but H18OCO is observed as well, typically at the level of 10%-20% that of HOC18O; the opposite propensity is found for the 18OH + CO reaction. DO + C18O yields similar ratios between DOC18O and D18OCO as those found for OH + C18O, suggesting that some fraction of HOCO (or DOCO) may be formed from the back-reaction H + CO2, which, at the high pressure of our gas expansion, can readily occur. The large 13C Fermi-contact term (aF) for trans- and cis-HO13CO implicates significant unpaired electronic density in a σ-type orbital at the carbon atom, in good agreement with theoretical predictions. To conclude, by correcting the experimental rotational constants for zero-point vibration motion calculated theoretically using second-order vibrational perturbation theory, precise geometrical structures have been derived for both isomers.},
doi = {10.1063/1.4944070},
journal = {Journal of Chemical Physics},
number = 12,
volume = 144,
place = {United States},
year = {2016},
month = {3}
}