Electron spin resonance of VO 2+ radical-ion in sub- and supercritical water

. [Display omitted] ► ESR spectra of VO 2+ radical-ions in sub- and supercritical water are observed. ► At subcritical region HFS spectrum components are broadened. ► Near T c ESR line with Δ H pp ∼ 300 G is observed due to high local ion concentration. Electron spin resonance (ESR) spectra of VO 2+ radical-ions in sub- and supercritical water are observed. Upon increasing the temperature from 20 to 100 °C, the fine structure line widths in the ESR spectra of the vanadyl ion are observed to be reduced that is associated with the effective averaging of the g-factor anisotropy and the hyperfine interaction. With further increasing the temperature, the spectrum components of the hyperfine structure are broadened significantly resulting in the unresolved low-intensity line in supercritical water with Δ H pp ∼ 300 G. The data obtained allow behavior peculiarities of the paramagnetic VO 2+ ions in sub- and supercritical water including rotational dynamics and spin exchange between the radicals to be elucidated. The registration of the unresolved low-intensity line in supercritical conditions points to an increase in the local ion concentration in the system that can be an initial stage for the formation of vanadium-based particles in supercritical conditions. The study demonstrates that ESR is the powerful tool to investigate properties of sub- and supercritical water in situ.