Enthalpies of Formation for Criegee Intermediates: A Correlation Energy Convergence Study

Criegee intermediates, formed from the ozonolysis of alkenes, are thought to have a role in atmospheric chemistry, fromforming acid rain to impacting the oxidizing capacity of the troposphere. Although studies have been conducted sincetheir discovery in 2008, the synthesis of these species in the laboratory has ushered in a new wave of investigationsof these structures, both theoretically and experimentally. In some of these theoretical studies, high-order correctionsfor correlation energy are included to account for the mid multi-reference character found in these systems. Many ofthese studies include a focus on kinetics; therefore calculated energies should be accurate (<1 kcal/mol in error). Inthis research, we compute the enthalpies of formation for a small set of Criegee intermediates, including higher-ordercoupled cluster corrections for correlation energy up to CCSDTQ(P). The enthalpies of formation for formaldehydeoxide, anti-acetaldehyde oxide, syn-acetaldehyde oxide, and acetone oxide are presented at 0 K as 26.5 kcal mol−1,15.6 kcal mol−1, 12.2 kcal mol−1, and 0.1 kcal mol−1, respectively. Additionally, we do not recommend the CCSDT(Q)energy correction, as it is approximately twice as large as that of the full CCSDTQ. Half of the CCSDT(Q) energycorrection may be included as a reliable, cost-effective estimation of CCSDTQ energies for Criegee intermediates.