Electron spin resonance study of the superoxide ion in melt-recrystallized strontium chloride

Abstract

An e.s.r. spectrum in melt-recrystallized SrCl₂ single crystals has a fully anisotropic g-tensor with principal values 2.0028, 2.0093 and 2.053 in directions oriented in the crystal as [110], and [110] and [001]. The spectrum is ascribed to O^–₂ in a site of D_2h symmetry between two anion vacancies, and interacting with two Sr²⁺ ions so that the unpaired electron resides in a B_2g orbital localized mainly on the O^–₂. The crystal field splitting Δ between B_2g and B_3g(O₂π_g(x) and π_g(y) mixed with Sr 4d) is about 40 times the spin-orbit coupling constant, i.e. about 0.9 eV. When Δ is so large, the orbital angular momentum reduction parameter cannot be estimated accurately from the g-tensor.