Spin Hamiltonian of 51V2+ in MgO, as Derived from Electron Nuclear Double Resonance

The electron nuclear double resonance spectrum of ⁵¹V²⁺ diluted in a single crystal of MgO has been measured at 4.2° and 77°K. The spin‐Hamiltonian parameters have been determined, including an additional hyperfine contribution of the type $S^{3}I$ . Perturbation theory up to the fourth order has been used to calculate the latter term as a result of interactions of the ground orbital singlet with higher orbital levels.