Vibronic Effects in the Electron Paramagnetic Resonance ofMn++in Ca(OH)2

The temperature variation of the spin-Hamiltonian parameters of ${\mathrm{Mn}}^{++}$ in Ca${\mathrm{}\left(\mathrm{OH}\right)\mathrm{}}_2$ single crystals was studied. The parameters $b_2^0\mathrm{}(=D)\mathrm{}$ and the isotropic part of the hyperfine-structure tensor $A$ showed marked variation in the range 80-800°K. $b_2^0$ showed a reversal of sign around 450°K. The theory of orbit-lattice interaction and the theory of covalent reduction of $A$ through spin polarization was applied to the interpretation of the temperature variance of $A$. The temperature variations of $b_2^0$ were interpreted as originating from the phonon modulations of the crystal field. The calculated values were comparable to the experimental values. Implicit temperature variations of $b_2^0$ were also found to be significant. Included also are the results of the velocities of sound in Ca${\mathrm{}\left(\mathrm{OH}\right)\mathrm{}}_2$ as functions of temperature.