Kinetics of the simplest Criegee intermediate reaction with ozone studied by mid-infrared quantum cascade laser spectrometer

TL;DR

This study measures the reaction rate of the simplest Criegee intermediate, CH$_2$OO, with ozone using mid-infrared quantum cascade laser spectroscopy, revealing discrepancies with theoretical predictions and implications for atmospheric chemistry.

Contribution

First direct measurement of CH$_2$OO reaction rate with ozone at 298 K, challenging previous theoretical estimates and informing atmospheric ozonolysis processes.

Findings

Measured rate coefficient at 298 K: (6.7±0.5)×10⁻¹⁴ cm³/sec

Reaction rate is pressure-independent from 30 to 100 Torr

Results suggest previous ab initio calculations are significantly inaccurate

Abstract

The kinetics of CH$_2$OO reaction with ozone has been studied by monitoring CH$_2$OO with time-resolved infrared (IR) absorption spectroscopy, which utilized fast chirped IR pulse train from a quantum cascade laser [J. Chem. Phys. 146, 244302 (2017)]. CH$_2$OO was prepared by photolyzing a gas mixture of CH$_2$I$_2$/O$_2$/O$_3$ at 352 nm; the photolysis wavelength was chosen to minimize the photodissociation of O$_3$. The measured rate coefficient at 298 K and 30 Torr is (6.7$\pm$0.5)x10$^{-14}$ cm$^3$sec$^{-1}$, independent of pressure from 30 to 100 Torr. The result indicates that previous ab initio calculations either underestimated or overestimated this reaction rate by one order of magnitude or more. The result also implies that in laboratory studies of ozonolysis of alkenes, the reaction of Criegee intermediate with ozone may play a role. However, this reaction would not compete with other CH$_2$OO sinks in the atmosphere.