Overlapping photo-ionized doubly excited resonance series for Li+ ion

Based on two different approaches, the B-spline-based K-matrix method and the eigenchannel R-matrix method, we present a detailed theoretical study on the photoionization from the ground and bound excited 1 s 2 s 1 S and 1 s 2 p 1 P states of an Li+ ion to continua between the N = 2 and N = 3 thresholds, dominated by overlapping doubly excited resonance series embedded in multiple singly ionized channels. The nearly identical theoretical spectra from these two different calculations, together with the excellent agreement between the length and velocity results, suggests that our study has successfully led to a reliable estimate of the Li+ photoionization spectra. In addition to identifying all overlapping doubly excited autoionization series, our calculated spectrum is in good agreement with the only observed data for two broad resonances. Our study has also shown that the strong interaction between neighboring resonances from different resonance series, which is responsible for the level crossing for in the He atom, is substantially smaller due to a stronger nuclear attraction to atomic electrons for the two-electron ions.