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Kinetics of the Reaction Between the Criegee Intermediate CH2OO and NO2: Experimental Measurements and Comparison with Theory

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Kinetics of the gas phase reaction between the stabilized Criegee intermediate formaldehyde oxide (CH 2 OO) and nitrogen dioxide (NO 2 ) have been measured using laser flash photolysis of CH 2 I 2 /O 2 /N 2 /NO 2 mixtures coupled with time-resolved broadband ultraviolet absorption spectroscopy. Experiments were performed in N 2 under pseudo-first-order conditions at temperatures between 242 and 353 K and pressures in the range 25 to 300 Torr. The kinetics of CH 2 OO + NO 2 are independent of pressure, with a mean rate coefficient of k 1 = (1.24 ± 0.22) × 10 –12 cm 3 s –1 at 298 K, where the uncertainty represents a combination of the 1σ statistical error and the systematic errors resulting from uncertainties in gas flow rates and in the concentration of NO 2 . Measurements indicate upper limits of <5% for production of NO 3 and <5% for production of NO, and further studies of product yields are warranted. In contrast to expectations from theory, the kinetics of CH 2 OO + NO 2 display a negative temperature dependence that can be described by k 1 = (1.07 ± 0.02) × 10 –12 × ( T /298) −(2.9±0.2) cm 3 s –1 . Analysis using the Master Equation Solver for Multi-Energy well Reactions is able to reproduce a negative temperature dependence for the reaction if significant changes to barrier heights are made, but the overall agreement between the experiment and theory remains poor. This work highlights the challenges associated with calculations for systems with significant multi-reference character.

Source: The Journal of Physical Chemistry A

DOI: 10.1021/acs.jpca.4c08203