Allowed and Forbidden Transitions in the Electron Spin Resonance of Mn²⁺ in CaSO₄

The allowed and forbidden ESR lines of Mn ²⁺ in CaSO ₄ have been studied. The observed hyperfine constants ( A _z =-99.1 gauss, A _x = A _y =-99.7 gauss) indicate strong ionicity of this crystal. The expressions for the separations of the forbidden doublets in the M =±3/2↔±1/2 transitions were obtained and compared with the experimental results. The intensity of the forbidden transitions due to cross terms ( E S _z S _± )(\(AS_{\mp}I_{\pm}\)) was found to obey \(({\sin}2\varpsi)^{2}\) rule.