Vacancy-Mn2+Pair Spectra in Alkali Chlorides

An attempt has been made to understand the fine-structure constants of the vacancy-associated-${\mathrm{Mn}}^{2+}$ complexes corresponding to spectra ${\mathrm{III}}_1$ and ${\mathrm{III}}_2$ observed by Watkins in NaCl and KCl. The point-charge contributions arising from the mechanisms which were not considered previously are included in our treatment. The role of overlap and/or covalency effects are analyzed by calculations. Assuming the lattice distortions in accordance with the available calculations, the theoretical values of the fine-structure constants are compared with the experimental values. For spectra ${\mathrm{III}}_1$ and ${\mathrm{III}}_2$ the $D$ and $E$ values are smaller than the experimental values but they agree in sign if one considers point-charge and overlap effects. The inclusion of covalency effects brings, in general, the calculated values into better agreement with experiment. Some conclusions have also been drawn regarding the distortion of the lattice in order to improve the calculated values.