6 research outputs found

    Low-Temperature Synchrotron Photoionization Study of 2‑Methyl-3-buten-2-ol (MBO) Oxidation Initiated by O(<sup>3</sup>P) Atoms in the 298–650 K Range

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    This work studies the oxidation of 2-methyl-3-buten-2-ol initiated by O­(<sup>3</sup>P) atoms. The oxidation was investigated at room temperature, 550, and 650 K. Using the synchrotron radiation from the Advanced Light Source (ALS) of the Lawrence Berkley National Laboratory, reaction intermediates and products were studied by multiplexed photoionization mass spectrometry. Mass-to-charge ratios, kinetic time traces, photoionization spectra, and adiabatic ionization energies for each primary reaction species were obtained and used to characterize their identity. Using electronic structure calculations, potential energy surface scans of the different species produced throughout the oxidation were examined and presented in this paper to further validate the primary chemistry occurring. Branching fractions of primary products at all three temperatures were also provided. At room temperature only three primary products formed: ethenol (26.6%), acetaldehyde (4.2%), and acetone (53.4%). At 550 and 650 K the same primary products were observed in addition to propene (5.1%, 11.2%), ethenol (18.1%, 2.8%), acetaldehyde (8.9%, 5.7%), cyclobutene (1.6%, 10.8%), 1-butene (2.0%, 10.9%), <i>trans</i>-2-butene (3.2%, 23.1%), acetone (50.4%, 16.8%), 3-penten-2-one (1.0%, 11.5%), and 3-methyl-2-butenal (0.9%, 2.5%), where the first branching fraction value in parentheses corresponds to the 550 K data. At the highest temperature, a small amount of propyne (1.0%) was also observed

    Synchrotron Photoionization Investigation of the Oxidation of Ethyl <i>tert</i>-Butyl Ether

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    The oxidation of ethyl <i>tert</i>-butyl ether (ETBE), a widely used fuel oxygenated additive, is investigated using Cl atoms as initiators in the presence of oxygen. The reaction is carried out at 293, 550, and 700 K. Reaction products are probed by a multiplexed chemical kinetics photoionization mass spectrometer coupled with the synchrotron radiation produced at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory. Products are identified on the basis of mass-to-charge ratio, ionization energies, and shape of photoionization spectra. Reaction pathways are proposed together with detected primary products

    Investigation of Oxidation Reaction Products of 2‑Phenylethanol Using Synchrotron Photoionization

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    A photolytically Cl-initiated oxidation reaction of 2-phenylethanol (2PE) was carried out at the Advanced Light Source (ALS) in the Lawrence Berkeley National Laboratory. Using the multiplex photoionization mass spectrometer, coupled with the tunable vacuum ultraviolet radiation of the ALS, data were collected at low pressure (4–6 Torr) and temperature (298–550 K) regimes. Data analysis was performed via characterization of the reaction species photoionization spectra and kinetic traces. Products and reaction pathways are also computed using the CBS-QB3 composite method. The present results suggest primary products <i>m</i>/<i>z</i> = 30 (formaldehyde), 106 (benzaldehyde), and 120 (phenylacetaldehyde) at 298 K, and <i>m</i>/<i>z</i> = 120 (phenylacetaldehyde) at 550 K. Branching fractions at room temperature are 27 ± 6.5% for formaldehyde, 24 ± 4.5% for benzaldehyde, and 25 ± 5.8% for phenylacetaldehyde and 60 ± 14% for phenylacetaldehyde at 550 K

    Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO<sub>2</sub>‑Elimination Channels

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    Cl-initiated oxidation reactions of three small-chain methyl esters, methyl propanoate (CH<sub>3</sub>CH<sub>2</sub>COOCH<sub>3</sub>; MP), methyl butanoate (CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>COOCH<sub>3</sub>; MB), and methyl valerate (CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>COOCH<sub>3</sub>; MV), are studied at 1 or 8 Torr and 550 and 650 K. Products are monitored as a function of mass, time, and photoionization energy using multiplexed photoionization mass spectrometry coupled to tunable synchrotron photoionization radiation. Pulsed photolysis of molecular chlorine is the source of Cl radicals, which remove an H atom from the ester, forming a free radical. In each case, after addition of O<sub>2</sub> to the initial radicals, chain-terminating HO<sub>2</sub>-elimination reactions are observed to be important. Branching ratios among competing HO<sub>2</sub>-elimination channels are determined via absolute photoionization spectra of the unsaturated methyl ester coproducts. At 550 K, HO<sub>2</sub>-elimination is observed to be selective, resulting in nearly exclusive production of the conjugated methyl ester coproducts, methyl propenoate, methyl-2-butenoate, and methyl-2-pentenoate, respectively. However, in MV, upon raising the temperature to 650 K, other HO<sub>2</sub>-elimination pathways are observed that yield methyl-3-pentenoate and methyl-4-pentenoate. In each methyl ester oxidation reaction, a peak is observed at a mass consistent with cyclic ether formation, indicating chain-propagating OH loss/ring formation pathways via QOOH intermediates. Evidence is observed for the participation of resonance-stabilized QOOH in the most prominent cyclic ether pathways. Stationary point energies for HO<sub>2</sub>-elimination pathways and select cyclic ether formation channels are calculated at the CBS-QB3 level of theory and assist in the assignment of reaction pathways and final products

    Synchrotron Photoionization Measurements of OH-Initiated Cyclohexene Oxidation: Ring-Preserving Products in OH + Cyclohexene and Hydroxycyclohexyl + O<sub>2</sub> Reactions

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    Earlier synchrotron photoionization mass spectrometry experiments suggested a prominent ring-opening channel in the OH-initiated oxidation of cyclohexene, based on comparison of product photoionization spectra with calculated spectra of possible isomers. The present work re-examines the OH + cyclohexene reaction, measuring the isomeric products of OH-initiated oxidation of partially and fully deuterated cyclohexene. In particular, the directly measured photoionization spectrum of 2-cyclohexen-1-ol differs substantially from the previously calculated Franck–Condon envelope, and the product spectrum can be fit with no contribution from ring-opening. Measurements of H<sub>2</sub>O<sub>2</sub> photolysis in the presence of C<sub>6</sub>D<sub>10</sub> establish that the addition–elimination product incorporates the hydrogen atom from the hydroxyl radical reactant and loses a hydrogen (a D atom in this case) from the ring. Investigation of OH + cyclohexene-4,4,5,5-<i>d</i><sub>4</sub> confirms this result and allows mass discrimination of different abstraction pathways. Products of 2-hydroxycyclohexyl-<i>d</i><sub>10</sub> reaction with O<sub>2</sub> are observed upon adding a large excess of O<sub>2</sub> to the OH + C<sub>6</sub>D<sub>10</sub> system

    Synchrotron Photoionization Study of Mesitylene Oxidation Initiated by Reaction with Cl(<sup>2</sup>P) or O(<sup>3</sup>P) Radicals

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    This work studies the oxidation of mesitylene (1,3,5-trimethylbenzene) initiated by O­(<sup>3</sup>P) or Cl­(<sup>2</sup>P) atoms. The O­(<sup>3</sup>P) initiated mesitylene oxidation was investigated at room temperature and 823 K, whereas the Cl-initiated reaction was carried out at room temperature only. Products were probed by a multiplexed chemical kinetics photoionization mass spectrometer using the synchrotron radiation produced at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory. Reaction products and intermediates are identified on the basis of their time behavior, mass-to-charge ratio, ionization energies, and photoionization spectra. Branching yields are derived for the O-initiated reaction at 823 K and the Cl-initiated reaction at room temperature. Reaction schematics are proposed and presented