Nuclear-Motion Corrections to the Fine Structure of Helium

The motion of the nucleus yields numerically important order $\frac{m}{M_{\mathrm{He}}}$ corrections to the fine structure of the helium atom. We present here the derivation of such corrections applied to the $2{}_{}{}^3{}_{}{}^{}P$ fine-structure splittings in ${\mathrm{He}}^4$.