Study of the vibronic effects from the Zeeman-field-induced Mössbauer spectra ofFe2+ions in octahedral symmetry. I. The effective Hamiltonian formalism

The importance of the Zeeman-field-induced quadrupole and hyperfine interactions in Jahn-Teller active ions is demonstrated with particular reference to ${\mathrm{Fe}}^{2+}$ in octahedral crystals such as CaO and KMg${\mathrm{F}}_3$. An effective electron nuclear Hamiltonian is derived from general symmetry principles, whose parameters are calculated by perturbation procedure, incorporating the vibronic effects in terms of Ham reduction factors between spin-orbit states. Relevant theoretical expressions for the Mössbauer transitions are given so that these parameters can be determined experimentally from the analysis of the Mössbauer spectra.