Properties of the combination harmonic in spectra of primary electron spin echo envelope modulation of orientationally selected disordered systems. Application to aqua-oxovanadium complexes

The properties of the sum combination (ν_α + ν_β) harmonic in the primary electron spin echo envelope modulation for systems with large g factor and hyperfine interaction anisotropy are investigated. The influence of the hyperfine interaction (HFI) parameters in the weak HFI limit on the magnitude of the shift of the combination harmonic away from the double Zeeman frequency of the nucleus are examined together with the quadrupole splitting of this line for a deuterium nucleus. The theoretical results are used for the analysis of the electron spin echo envelope modulation spectra of oxovanadium-aqua complexes with H₂O and D₂O in frozen solution, which yield the HFI parameters of the ligand water protons. The structural information based on these HFI data are discussed in comparison with previous single crystal and powder electron nuclear double resonance results.