Theoretical study of the lowestΣg+1doubly excited state ofH2

Abstract

The energy and width of the ${}_{}{}^1{}_{}{}^{}\sigma _u^2{}_{}{}^{}{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ state of ${\mathrm{H}}_2$ are calculated using Feshbach projection operators and the Stieltjes moment method. The results are compared with an analysis of the double minima in the potential-energy curves of the ${}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ Rydberg states. The doubly excited ${}_{}{}^1{}_{}{}^{}\sigma _u^2{}_{}{}^{}$ configuration is unstable with respect to autoionization for $R<\mathrm{}2.65\mathrm{}{a}_0$, and the autoionization rate is sensitive to both the value of the internuclear separation and the energy of the emitted electron.