Isomerization and Dissociation of (CH3)2COO Criegee Intermediate: Ab Initio and RRKM Study

Abstract

Criegee Intermediates (CIs), or carbonyl oxides, arise due to ozonolysis of alkenes, which are typical anthropogenic air pollutants. They play an important role in many chemical reactions occurring both in the lower and in the upper atmosphere of the Earth. Dissociation products of CIs may interact with other atmospheric compounds to produce hydroxyl (OH) radicals and other chemically active substances. Probably, these reactions are responsible for formation of nitric and sulfuric acids in the atmosphere. In the troposphere, CIs dissipate their initial internal energy through collisions with the bath atmospheric gases, and interact with chemically active atmospheric molecules. In the stratosphere and mesosphere carbonyl oxides can decay into chemically active fragments, which then trigger multiple secondary reactions. In this work the main dissociation reactions of (CH₃)₂COO Criegee intermediate molecule were studied. For that, ab initio B3LYP/CCSD(T) potential energy surface (PES) calculations have been performed followed by the estimation of rate constants and products yield by the RRKM method. It was found that the most probable dissociation products are OH, CH₃COCH₂, CH₃, and CH₃OCO radicals, as well as ethane and CO₂.