Ab Initio Quantum Chemical Studies of the Formaliminoxy (CH_2NO) Radical: 1. Isomerization Reactions

摘要

A detailed ab initio quantum chemical investigation of the potential energy surface associated with the isomerization reactions of the formaldiminoxy (CH_2NO) radical is reported. CH_2NO(~2A') is the direct product of the reaction between triplet methylene and "prompt" nitric oxide. The quantum chemical calculations were performed at the Gaussian-2 (G2), CASSCF, CASPT2, and QCISD(T) levels of theory using basis sets that range from cc-pVDZ and cc-pVTZ up to the 6-311+G(3df,2p) of G2. A total of 11 isomers (plus 9 rotamers) and 28 transition states linking them are identified and characterized on the potential energy surfaces. The isomers and their rearrangement reactions are conveniently divided into two classes: those with CNO-and NCO-chain backbones. The latter class of molecules are generally more stable, with the NH_2CO isomer being the most stable with a predicted heat of formation of -3.6 +- 1 kcal/mol. Interconversion between the two groups occurs via a cyclic isomer of CH_2NO. The energetics of the various isomerization pathways are expected to influence the subsequent dissociation reactions of the formaldiminoxy isomers.