Matrix‐Isolation Electron Paramagnetic Resonance Studies of Radical Ions and Neutral Radicals Generated by Radiolysis of Organic Molecules at Cryogenic Temperatures

Electron paramagnetic resonance (EPR) spectroscopy has long been widely utilized to investigate, characterize, and monitor highly reactive paramagnetic chemical species generated in materials upon exposure to ionizing radiation. This personal account presents EPR observations and spectral analyses of several fundamental paramagnetic species, including cations, anions, and neutral radicals, isolated using a low-temperature solid matrix isolation (MI) technique combined with radiation exposure, a method in which the author has extensive experience. These findings are not only of significant interest in the field of molecular science but also demonstrate the utility of the MI technique as a laboratory-based approach to exploring chemical evolution in space. Recent density functional theory analyses, which reveal a second-order Jahn-Teller distortion, suggest that the stability of the distorted structure of the silacyclohexane radical cation is considerably less pronounced than previously indicated by Hartree-Fock-based theoretical calculations. Furthermore, EPR results for the perfluorocubane radical anion, a species that has recently attracted significant attention, are also presented.