Determination of the hyperfine coupling constant and zero-field splitting in the ESR spectrum of Mn(2+) in calcite

The hyperfine coupling constant (A in units of energy or A' in units of magnetic field) and zero-field splitting (D in units of energy or D' in units of magnetic field) in the ESR spectrum of Mn(2+) in calcite were determined. The spreading of the non-central allowed transitions |3/2, m --> |5/2, m, |1/2, m --> |3/2, m, |-3/2, m --> |-1/2, m and |-5/2, m --> |-3/2, m was analysed and the experimental transitions were attributed. Particular relevance was given to the difference between the two types of resonances, shoulder or divergence, and to their origin (M, m). The analysis explains the presence of a weak shoulder between each of the five central doublets |-1/2, m --> |1/2, m. Six independent methods for calculating the hyperfine coupling constant and five methods for calculating the zero-field splitting, based on the analysis of the allowed and forbidden transitions, were provided. The values of the hyperfine coupling constant range from -93.9 to -94.6 G and those of the zero-field splitting range from -79.5 to -80.5 G. A critical evaluation of the advantages and drawbacks of the 11 methods is included: the best value for A' is -94.30 G and that for D' is -79.95 G.