Relativistic effects of the1s2s2pP4ofHe−

With the use of an accurate nonrelativistic wave function, the relativistic effects of the ${\mathrm{He}}^{-}$ $1s2s2p{}_{}{}^4{}_{}{}^{}P$ state are computed. These include the mass-correction term, Darwin term, and retardation and mass-polarization effects. The calculated result enables us to significantly reduce the uncertainty of the electron affinity given by Bunge and Bunge. To assist future experimental measurement on the fine structure of this ion, the expectation values of the spin-orbit, spin-other-orbit, and spin-spin operators are also calculated.