Heats of formation of the Criegee formaldehyde oxide and dioxirane

CCSD(T)/CBS calculations plus corrections predict the heats of formation of formaldehyde O-oxide 1 and dioxirane 2: Δ H f 0 ( CH 2 OO, 1 ) = 28.1 and 26.4 kcal/mol, and Δ H f 0 ( CH 2 O 2 , 2 ) = 3.0 and 1.2 kcal/mol at 0 K and 298 K, respectively. The adiabatic ionization energies are IEa(1) = 9.98 eV and IEa(2) = 10.82 eV. Protonation of carbonyl oxide takes place at terminal oxygen with a proton affinity of PA(1) = 203.5 ± 1.0 kcal/mol. The vertical triplet state 3A′ of 1 is located at 1.82 eV above the ground state (with errors of ±1.0 kcal/mol or ±0.05 eV). The parent Criegee intermediate is unstable with respect to O–O bond cleavage but becomes more stable upon ionization.