Calculation of resonances in doubly excited helium using the stabilization method

Mandelshtam, Ravuri, and Taylor [Phys. Rev. Lett. 70, 1932 (1993)] have recently proposed a novel approach for the calculation of resonance states in one- and two-channel problems. We show that a modification of this approach, suitable for stabilization calculations, can yield both the resonance position and width for doubly excited states in two-electron systems. This provides a simple and numerically efficient method to calculate the spectral density of states. In the region of overlapping ${}_{}{}^1{}_{}{}^{}$ ${\mathit{S}}^{\mathit{e}}$ Rydberg manifolds, we find very narrow resonances associated with the symmetric excitation of both electrons. The mechanism for the occurrence of such resonances is discussed.