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

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.