Formation and Evolution of H 2 C 3 O +• Radical Cations: A Computational and Matrix Isolation Study

The family of isomeric H C O radical cations is of great interest for physical organic chemistry and chemistry occurring in extraterrestrial media. In this work, we have experimentally examined a unique synthetic route to the generation of H C O from the C H ···CO intermolecular complex and also considered the relative stability and monomolecular transformations of the H C O isomers through high-level calculations. The structures, energetics, harmonic frequencies, hyperfine coupling constants, and isomerization pathways for several of the most important H C O isomers were calculated at the UCCSD(T) level of theory. The complementary FTIR and EPR studies in argon matrices at 5 K have demonstrated that the ionized C H ···CO complex transforms into the -HCCHCO isomer, and this latter species is supposed to be the key intermediate in further chemical transformations, providing a remarkable piece of evidence for kinetic control in low-temperature chemistry. Photolysis of this species at λ = 410-465 nm results in its transformation to the thermodynamically most stable H CCCO isomer. Possible implications of the results and potentiality of the proposed synthetic strategy to the preparation of highly reactive organic radical cations are discussed.