Doubly excited resonance structures in He photoionization from1s2s1,3Smetastable states

Abstract

The resonant structures corresponding to selected He sp, 2n{sup {plus_minus}} and 2pnd{sup 1,3}P{sup o} autoionization series below the He{sup +} N=2 threshold, following photoionization from 1s2s{sup 1,3}S metastable states, are examined in detail. Theoretical photoionization cross sections, calculated using a B-spline-based configuration-interaction approach with a length-velocity agreement better than 1{percent}, are presented. A sign change in Fano profile parameters q in 1s2s{sup 1}S{r_arrow}sp,2n{sup +}{sup 1}P transitions along the 2n{sup +} autoionization series is identified and analyzed. {copyright} {ital 1997} {ital The American Physical Society}