Formation and Evolution of H2C3O+• Radical Cations: A Computational and Matrix Isolation Study

Astrochemically Relevant Radicals and Radical-Molecule Complexes: A New Insight from Matrix Isolation

The reactive open-shell species play a very important role in the radiation-induced molecular evolution occurring in the cold areas of space and presumably leading to the formation of biologically relevant molecules. This review presents an insight into the mechanism of such processes coming from matrix isolation studies with a main focus on the experimental and theoretical studies performed in the author's laboratory during the past decade. The radicals and radical cations produced from astrochemically relevant molecules were characterized by Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) spectroscopy. Small organic radicals containing C, O, and N atoms are considered in view of their possible role in the formation of complex organic molecules (COMs) in space, and a comparison with earlier results is given. In addition, the radical-molecule complexes generated from isolated intermolecular complexes in matrices are discussed in connection with their model significance as the building blocks for COMs formed under the conditions of extremely restricted molecular mobility at cryogenic temperatures.

An EPR study on the radiolysis of isolated ethanol molecules in solid argon and xenon: matrix control of radiation-induced generation of radicals in cryogenic media

This paper addresses the basic question of the impact of a chemically inert environment on the radiation-induced transformations of isolated organic molecules in icy media at cryogenic temperatures with possible implications for astrochemical issues. The radicals produced by X-ray irradiation of isolated ethanol molecules (C₂H₅OH and CH₃CD₂OH) in solid argon and xenon matrices at 7 K were characterized by electron paramagnetic resonance (EPR) spectroscopy. It was shown that methyl (CH₃˙) and formyl (HCO˙) radicals resulting from the C-C bond cleavage were mainly produced in the case of solid argon, which was attributed to the significant role of "hot" ionic fragmentation and inefficient energy dissipation to medium. In contrast, irradiation in xenon results in the predominant formation of α-hydroxyethyl radicals (CH₃˙CHOH or CH₃˙CDOH(D) in the cases of C₂H₅OH and CH₃CD₂OH, respectively). Remarkably, the experiments with selectively deuterated ethanol provide strong indirect evidence for the primary formation of ethoxy (CH₃CD₂O˙) radicals due to O-H bond cleavage, which convert to the α-hydroxyethyl radicals due to isomerization occurring at 7 K. The α-hydroxyethyl radicals adopt a specific rigid conformation with a non-rotating methyl group at low temperatures, which is an unusual effect for neutral CH₃˙CHX species, and exhibit free rotation in solid xenon only at ca. 65 K.