Thermochemistry of the smallest QOOH radical from the roaming fragmentation of energy selected methyl hydroperoxide ions

Journal Article · Fri Jul 20 00:00:00 EDT 2018 · Physical Chemistry Chemical Physics. PCCP

DOI:https://doi.org/10.1039/C8CP03168A· OSTI ID:1485834

Covert, Kyle J.  ^[1]; Voronova, Krisztina  ^[1]; Torma, Krisztián G.  ^[1]; Bodi, Andras  ^[2]; Zádor, Judit  ^[3]; Sztáray, Bálint  ^[1]

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1. Univ. of the Pacific, Stockton, CA (United States)
2. Paul Scherrer Institute, Villigen (Switzerland)
3. Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Here, the dissociative photoionization processes of methyl hydroperoxide (CH₃OOH) have been studied by imaging Photoelectron Photoion Coincidence (iPEPICO) spectroscopy experiments as well as quantum-chemical and statistical rate calculations. Energy selected CH₃OOH⁺ ions dissociate into CH₂OOH⁺, HCO⁺, CH₃⁺, and H₃O⁺ ions in the 11.4–14.0 eV photon energy range. The lowest-energy dissociation channel is the formation of the cation of the smallest “QOOH” radical, CH₂OOH⁺. An extended RRKM model fitted to the experimental data yields a 0 K appearance energy of 11.647 ± 0.005 eV for the CH₂OOH⁺ ion, and a 74.2 ± 2.6 kJ mol^-1 mixed experimental-theoretical 0 K heat of formation for the CH₂OOH radical. The proton affinity of the Criegee intermediate, CH₂OO, was also obtained from the heat of formation of CH₂OOH⁺ (792.8 ± 0.9 kJ mol^-1) to be 847.7 ± 1.1 kJ mol^-1, reducing the uncertainty of the previously available computational value by a factor of 4. RRKM modeling of the complex web of possible rearrangement-dissociation processes was used to model the higher-energy fragmentation. Supported by Born–Oppenheimer molecular dynamics simulations, we found that the HCO⁺ fragment ion is produced through a roaming transition state followed by a low barrier. Lastly, H₃O⁺ is formed in a consecutive process from the CH₂OOH⁺ fragment ion, while direct C–O fission of the molecular ion leads to the methyl cation.

• Research Organization: Sandia National Lab. (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000; NA0003525
• OSTI ID: 1485834
• Alternate ID(s): OSTI ID: 1462769
• Report Number(s): SAND-2018-12912J; PPCPFQ; 669829
• Journal Information: Physical Chemistry Chemical Physics. PCCP, Vol. 20, Issue 32; ISSN 1463-9076
• Publisher: Royal Society of Chemistry
• Country of Publication: United States
• Language: English

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