Spin-dependent interactions in Mn III3d5

An energy-level calculation of the $3d^5$ configuration of Mn III is carried out, including eleven newly observed energy levels. The calculation takes into account the "weak" spin-dependent interactions, namely the spin-other-orbit, the spin-spin, and the effective electrostatic-spin-orbit interactions, which are of special importance in the half-filled $3d$ shell. An excellent fit between the calculated and observed energy levels is obtained, with a mean error of 7 ${\mathrm{cm}}^{-1\mathrm{}}$, and a mean $o-c$ spread" of 3 ${\mathrm{cm}}^{-1\mathrm{}}$ per multiplet. A ratio between effective electrostatic-spin-orbit interaction parameters $Q^2$ and $Q^4$ is established for the first time.