ИСТИНА

The family of isomeric H2C3O+• radical cations is of great interest for physical organic chemistry and chemistry occurring in the extraterrestrial media. In this work, we have experimentally examined a unique synthetic route to the generation of H2C3O+• from the C2H2∙∙∙CO intermolecular complex and also considered the relative stability and monomolecular transformations of the H2C3O+• isomers through high-level ab initio calculations. Matrix samples were obtained by deposition of gaseous mixtures (C2H2/CO/Ng 1/3/1000; Ng = Ar, Kr, Xe) onto a cold KBr substrate mounted in a closed-cycle helium cryostat. The conditions of the deposition procedure were optimized to obtain a sufficient amount of the precursor 1:1 C2H2∙∙∙CO complex. The deposited matrices were irradiated with X-rays (effective energy ca. 20 keV) to different doses (up to 200 kGy) at 5 K. Photolysis of the irradiated samples was performed using appropriate LEDs (λD = 465 nm and λD = 410 nm). The radiation-induced products and intermediates were characterized by FTIR and EPR spectroscopy. The structures, energetics, harmonic frequencies, hyperfine coupling constants, and isomerization pathways for several most important H2C3O+• isomers were calculated at the UCCSD(T) level of theory. The complimentary FTIR and EPR studies in argon matrices at 5 K supported by the high- level ab initio calculations have demonstrated that ionized C2H2∙∙∙CO complex transforms into the E-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 the low-temperature chemistry. Photolysis of this species at λ = 410–465 nm results in its transformation to the thermodynamically most stable H2CCCO+• isomer. Possible implications of the results and potentiality of the proposed synthetic strategy to the preparation of highly reactive organic radical cations are discussed.