Isomer-Selective Detection of Keto-Hydroperoxides in the Low-Temperature Oxidation of Tetrahydrofuran

Journal Article · Wed Sep 04 00:00:00 EDT 2019 · Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

DOI:https://doi.org/10.1021/acs.jpca.9b07017· OSTI ID:1570293

Hansen, Nils ^[1]; Moshammer, Kai ^[2]; Jasper, Ahren W. ^[3]

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1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2. Physikalisch-Technische Bundesanstalt, Braunschweig (Germany)
3. Argonne National Lab. (ANL), Lemont, IL (United States)

Keto-hydroperoxides (KHPs) are reactive, partially oxidized intermediates that play a central role in chain-branching reactions during the gas-phase low-temperature oxidation of hydrocarbons and oxygenated species. Although multiple isomeric forms of the KHP intermediate are possible in complex oxidation environments when multiple reactant radicals exist that contain nonequivalent O₂ addition sites, isomer-resolved data of KHPs have not been reported. In this work, we provide partially isomer-resolved detection and quantification of the KHPs that form during the low-temperature oxidation of tetrahydrofuran (THF, cycl.-O–CH₂CH₂CH₂CH₂–). We describe how these short-lived KHPs were detected, identified, and quantified using integrated experimental and theoretical approaches. The experimental approaches were based on direct molecular-beam sampling from a jet-stirred reactor operated at near-atmospheric pressure and at temperatures between 500 and 700 K, followed by mass spectrometry with single-photon ionization via tunable synchrotron-generated vacuum-ultraviolet radiation, and the identification of fragmentation patterns. The interpretation of the experiments was guided by theoretical calculations of ionization thresholds, fragment appearance energies, and photoionization cross sections. On the basis of the experimentally observed and theoretically calculated ionization and fragment appearance energies, KHP isomers could be distinguished as originating from H-abstraction reactions from either the α-C adjacent to the O atom or the β-C atoms. Temperature-dependent concentration profiles of the partially resolved isomeric KHP intermediates were determined in the range of 500–700 K, and the results indicate that the observed KHP isomers are formed overwhelmingly (~99%) from the α-C THF radical. Furthermore, the comparisons of the partially isomer-resolved quantification of the KHPs to up-to-date kinetic modeling results reveal new opportunities for the development of a next-generation THF oxidation mechanism.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States); Sandia National Laboratories (SNL-CA), Livermore, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
• Grant/Contract Number: AC02-06CH11357; AC04-94AL85000
• OSTI ID: 1570293
• Alternate ID(s): OSTI ID: 1574362
• Report Number(s): SAND--2019-10051J; 678832
• Journal Information: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Journal Name: Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory Journal Issue: 38 Vol. 123; ISSN 1089-5639
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

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