Phys. Chem. Chem. Phys. : RESOLV member Prof. Dominik Marx presents terahertz (THz) spectroscopy methods to study the solvation dynamics of open-shell molecular radicals in water. Focusing on the nitroxide spin probe HMI (2,2,3,4,5,5-HexaMethylImidazolidin-1-oxyl), the study generalizes established spectral decomposition techniques—supermolecular solvation complex (SSC) and cross-correlation analysis (CCA)—to systems with unpaired electrons. Through this methodological advance, the authors assign the THz spectral contributions of HMI and its hydration shell, revealing that low-frequency spectral features are dominated by intramolecular motions of the radical itself, with minimal impact from solvation-site interactions. The work lays the groundwork for analyzing the vibrational solvation dynamics of other free radicals in aqueous environments.
