Line-Intensity Angular Dependence in Paramagnetic-Resonance Spectrum ofS-State Ions with Axial Crystalline Environments

An intensity spin operator that leads to a simple description of the intensity of electron-paramagnetic-resonance lines is derived in the case of comparable crystal field and hyperfine interactions. These theoretical results are compared with the descriptions given by the method of Bir and by first-order- perturbation calculations, then with experimental measurements on ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$: ${\mathrm{Mn}}^{2+}$ EPR spectra.