Kinetic studies of excited singlet oxygen atom O(¹D) reactions with ethanol

Abstract

The multichannel reaction of excited singlet oxygen atom with ethanol, O(1D) + C2H5OH (1), was studied in a photolysis flow reactor coupled with mid‐infrared Faraday rotation spectroscopy (FRS) and UV‐IR direct absorption spectroscopy (DAS) at 297 K with reactor pressures of 60, 120, and 150 Torr (bath He). The excited singlet oxygen atom was generated through the photolysis of O3 at 266 nm. The photon flux and O(1D) concentrations were determined by in situ actinometry based on O3 depletion. Temporal profiles of OH and H2O were monitored via DAS signals at ca. 3568.62 and 3568.29 cm−1, while temporal profiles of HO2 were measured via FRS signals at ca. 1396.90 cm−1. The branching ratios of the target reaction (1) were determined by fitting temporal profiles to simulations from an in‐house reaction mechanism. Two major reaction channels were identified as CH3CHOH + OH and CH3O + CH2OH, and their branching ratios were determined as 0.46 ± 0.12 and 0.42 ± 0.11, respectively. A specific HO2 + RO2 reaction between HO2 and O2CH2CH2OH (β‐RO2) at the low‐temperature range is estimated in this work as HO2 + O2CH2CH2OH ⟶ products with a rate constant of 7 × 10−12 cm3 molecule−1 s−1.

Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether

“…Details of the experimental method have been explained previously. 13,29,30,33 In the present work, O( 1 D) atoms are generated by pulsed Nd:YAG laser photolysis (∼140 mJ/pulse, 0.25 Hz) at 266 nm of a gas mixture containing DME, oxygen, ozone, and helium. In situ laser light actinometry is performed to determine the photon flux F (photons cm −2 ) and the absolute concentration of O( 1 D).…”

“…In our flow reactor system (shown in Figure (a)), we combine a pulsed laser photolysis scheme to generate O( 1 D) in a well-defined flow environment with a UV-IR laser spectroscopy scheme for time-dependent in situ detection and quantification of gas-phase species. Details of the experimental method have been explained previously. ,,, In the present work, O( 1 D) atoms are generated by pulsed Nd:YAG laser photolysis (∼140 mJ/pulse, 0.25 Hz) at 266 nm of a gas mixture containing DME, oxygen, ozone, and helium. In situ laser light actinometry is performed to determine the photon flux F (photons cm –2 ) and the absolute concentration of O( 1 D).…”

“…The branching fractions are significantly different from those found for the O( 1 D) reactions with alcohols and hydrocarbons, where OH is the dominant product. 30 Additional experimental descriptions, uncertainty quantification, and mechanism development are provided in the Supporting Information.…”

“…FRS provides interference-free detection of a molecule’s rovibrational transitions based on Zeeman splitting. Our previous work , has shown that FRS is a reliable detection technique for the precise characterization of the O­( 1 D)-sensitized HO 2 kinetics. The combination of UV-IR laser absorption spectroscopy and FRS provides a versatile diagnostic platform for investigating O­( 1 D) kinetics that overcomes the limitations of other methods in affording near-universal, time-dependent (μs time scale), isomer-specific detection and quantitation of products at different time scales.…”

“…Comparison of major kinetics pathways for O­( 1 D) reactions with dimethyl ether (upper half, as discussed in this work) and ethanol (lower half, as discussed in Zhong et al). The reaction conditions for the two cases are chosen to be the same as those in Figure .…”