ELECTRON-AFFINITY OF HELIUM (1S2S)-S-3

A configuration-interaction calculation with a carefully optimized orbital basis gives an upper bound Eu=-2.178040 a.u. (He) for the nonrelativistic energy Enr of the (1s2s2p)P04 metastable state of the He negative ion. Extensive studies of patterns of convergence for the energy show that Enr=-2.178074(10), which together with Pekeris' accurate Enr He (1s2s)S3 yields a nonrelativistic electron affinity Anr=77.4(3) meV. It is argued that the true electron affinity should not differ from Anr 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. © 1979 The American Physical Society.