Electron affinity of helium(1s2s)S3

Abstract

A configuration-interaction calculation with a carefully optimized orbital basis gives an upper bound $E_u=-2.178040\mathrm{}$ a.u. (He) for the nonrelativistic energy $E_{\mathrm{nr}}$ of the $\mathrm{}\left(1s2s2p\right)\mathrm{}{}_{}{}^4{}_{}{}^{}P_{}^0{}_{}{}^{}$ metastable state of the He negative ion. Extensive studies of patterns of convergence for the energy show that $E_{\mathrm{nr}}=-2.178074\mathrm{}\left(10\right)\mathrm{}$, which together with Pekeris' accurate $E_{\mathrm{nr}}$ $\mathrm{He}\mathrm{}\left(1s2s\right)\mathrm{}{}_{}{}^3{}_{}{}^{}S$ yields a nonrelativistic electron affinity $A_{\mathrm{nr}}=77.4\mathrm{}\left(3\right)\mathrm{}$ meV. It is argued that the true electron affinity should not differ from $A_{\mathrm{nr}}$ by more than ±0.2 meV. Good agreement with the less-precise experimental values is obtained. The present results, by allowing a recalibration of the experiments, will permit a significant increase in the accuracy of future experimental determinations of electron affinities below 300 meV.