EPR detection of the substitutionalH2−ion in magnesium oxide

EPR measurements and theoretical calculations are presented that show that stable, $S=\frac{1}{2}$, substitutional ${\mathrm{H}}^{2-}$ ions (a proton and three electrons trapped at an anion-vacancy site) are formed in MgO when a substitutional ${\mathrm{H}}^{-}$ ion traps an electron. Irradiation with blue (400 nm) light is found to be very effective in forming ${\mathrm{H}}^{2-}$ ions in MgO.