Strong magnetic-field effects on the states of the helium negative ion below the He(N=2)threshold

Abstract

Energy levels of the ${1s2l2l}^{\ensuremath{'}}{}^{2}{S}^{e}$ and ${}^{2,4}{P}^{e,o}$ states of the helium negative ion in magnetic-field strengths up to $4.7011\ifmmode\times\else\texttimes\fi{}{10}^{4}$ T are calculated by using the multiconfiguration interaction approach. The extended full core plus correlation (FCPC) method and the saddle-point technique are used to construct the nonrelativistic wave functions. We have observed that the field effects on the states considered are quite unusual. In the presence of a magnetic field, three previously unobserved stable states associated with the helium $1s2p{}^{1}P$ and $1s2s{}^{3}S$ thresholds are predicted. The possibility of attracting an extra electron by the parent ${1s}^{2}$ state is also analyzed in the low and medium regime $(\ensuremath{\beta}<~0.1$ a.u.). The opening of new decay channels of the ${1s2s}^{2}{}^{2}S$ resonance state connected with the higher threshold due to field effects is analyzed. Two significantly different resonance mechanisms for the ${1s2s}^{2}$ state are proposed and discussed briefly.