Issue 31, 2020

Dynamics of the reaction CH2I + O2 probed via infrared emission of CO, CO2, OH and H2CO

Abstract

The reaction CH2I + O2 has been widely employed recently for the production of the simplest Criegee intermediate CH2OO in laboratories, but the detailed dynamics of this reaction have been little explored. Infrared emission of several products of this reaction, initiated on irradiation of CH2I2 and O2 (∼8 Torr) in a flowing mixture at 308 or 248 nm, was recorded with a step-scan Fourier-transform spectrometer; possible routes of formation were identified according to the observed vibrational distribution of products and published theoretical potential-energy schemes. Upon irradiation at 308 nm, Boltzmann distributions of CO (v ≤ 5, J ≤ 19) with an average vibrational energy of 32 ± 3 kJ mol−1 and OH (v ≤ 3, J ≤ 5.5) with an average vibrational energy of 29 ± 4 kJ mol−1 were observed and assigned to the decomposition of HCOOH* to form CO + H2O and OH + HCO, respectively. The broadband emission of CO2 was simulated with two vibrational distributions of average energies (91 ± 4) and (147 ± 8) kJ mol−1 and assigned to be produced from the decomposition of HCOOH* and methylene bis(oxy), respectively. Upon irradiation of samples at 248 nm, the emission of OH and CO2 showed similar distributions with slightly greater energies, but the distribution of CO (v ≤ 11, J ≤ 19) became bimodal with average vibrational energies of (23 ± 4) and (107 ± 29) kJ mol−1, and branching (56 ± 5) : (44 ± 5). The additional large-v component is assigned to be produced from a secondary reaction HCO + O2 to form CO + HO2; HCO is a coproduct of OH. The branching between CO and OH is (50 ± 5) : (50 ± 5) at 308 nm and (64 ± 5) : (36 ± 4) at 248 nm, consistent with the mechanism according to which an additional channel to produce CO opens at 248 nm. Highly internally excited H2CO was also observed. With O2 at 16 Torr, the extrapolated nascent internal distributions are similar to those with O2 at 8 Torr except for a slight quenching effect.

Graphical abstract: Dynamics of the reaction CH2I + O2 probed via infrared emission of CO, CO2, OH and H2CO

Supplementary files

Article information

Article type
Paper
Submitted
10 Apr 2020
Accepted
11 Jul 2020
First published
13 Jul 2020

Phys. Chem. Chem. Phys., 2020,22, 17540-17553

Dynamics of the reaction CH2I + O2 probed via infrared emission of CO, CO2, OH and H2CO

T. Chen and Y. Lee, Phys. Chem. Chem. Phys., 2020, 22, 17540 DOI: 10.1039/D0CP01940B

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