The 9 and 33 GHz EPR Spectra of Mn 2+ Impurity Ions in Polycrystalline Calcite-Noncentral Transitions

Abstract

The first systematic 9.2 and 33.3 GHz. 293 K EPR study of the noncentral Δ M = ±1, Δ m = 0 HFS transitions due to Mn 2+ impurity ions in natural and synthetic polycrystalline calcite and the calcite mineral component in a coal sample is reported. Computer simulation programs for both the spin-Hamiltonian third-order perturbation and the diagonalization methods were used to study the observed spectra quantitatively. It is shown that the spin-Hamiltonian diagonalization method could simulate the polycrystalline EPR spectrum within the experimental error of 0.06 mT whereas the perturbation method had a maximum error of 0.6 mT. Simulations of the noncentral transition spectra using the diagonalization method enabled the spin-Hamiltonian ZFS parameters to be determined more accurately and the values of the HFS parameter A and the g factor obtained previously from the central transitions to be verified. It is found that the trigonal ZFS C 4 0, C 4 3, and S 4 3 terms, which have been ignored previously, play an important role in characterizing the Mn 2+ impurity ion EPR spectrum in polycrystalline calcite, and that the noncentral transition spectrum cannot be simulated accurately without including the effect of the spin-spin interaction lineshape broadening on the different FS transitions. The detailed spectral structure of the experimental noncentral transitions and lineshapes has been simulated accurately. This enabled all of the local maxima in the first Fourier absorption coefficient a 1 spectrum which are due to noncentral transitions for a polycrystalline sample to be identified in the region outside the central transitions. These computer simulations are also used to analyze the Mn 2+ spectrum in the calcite mineral component of an Alberta hv bituminous coal sample and to estimate its spin-Hamiltonian parameter distributions due to incomplete calcite microcrystallization.