Detailed mechanism and kinetics of the reaction of Criegee intermediate CH2OO with HCOOH investigated via infrared identification of conformers of hydroperoxymethyl formate and formic acid anhydride

• Published in: Physical chemistry chemical physics : PCCP Vol. 21; no. 38; pp. 21445 - 21455
• Main Authors: Chen-An, Chung, Jou, Wei Su, Yuan-Pern, Lee
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2019
• Subjects: Absorption spectra; Acidic oxides; Anharmonicity; Atmospheric chemistry; Coefficients; Computer simulation; Decay; Experiments; Formic acid; Hydrogen bonding; Infrared absorption; Infrared spectra; Irradiation; Mathematical models; Organic chemistry; Partial pressure; Photolysis; Reaction kinetics; Simulation
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c9cp04168k

The reaction of Criegee intermediate CH2OO with HCOOH is important in atmospheric chemistry, but its mechanism and kinetics are little investigated. We recorded time-resolved infrared absorption spectra of transient species produced upon irradiation at 308 nm of a flowing mixture of CH2I2/O2/N2/HCOOH at 298 K. Bands of CH2OO were observed initially upon irradiation; their decrease was accompanied with the appearance of several bands near 887, 925, 1052, 1115, 1170, 1342, 1391, and 1760 cm−1, assigned to the absorption of hydroperoxymethyl formate [HC(O)OCH2OOH, HPMF], that decreased in intensity at a later period with the appearance of absorption bands of the anti-conformer of formic acid anhydride [anti-(HCO)2O, FAN] near 998, 1101, 1767, and 1821 cm−1. The main contributions of the infrared absorption of HPMF are from an open-form conformer, but small contributions from the intramolecular hydrogen-bonded conformer that absorbs near 1070, 1170, and 1732 cm−1 were identified. Observed infrared spectra of both conformers of HPMF and anti-FAN agree satisfactorily with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3LYP/aug-cc-pVTZ method. We derived a rate coefficient for CH2OO + HCOOH to be k = (1.4 ± 0.3) × 10−10 cm3 molecule−1 s−1 from formation of HPMF. We found also that anti-FAN was produced mainly from the open-form conformer with rate coefficient k = (1460 ± 30) s−1; the intramolecular hydrogen-bonded conformer of HPMF is stable.