Photoionisation of helium

Abstract

The photoionisation cross section of helium is calculated including the 1s, 2s and 2p eigenstates and 3s, 3p and 3d pseudostates in an expansion of the ¹S^e initial and ¹P⁰ final wavefunctions. Good agreement is obtained with experiment and with other theories when the He⁺ ion is left in its ground state. In addition the position, width and shape of the 2s2p ¹P⁰ autoionisation state is accurately described by the theory. However, while the calculated ratio of the He⁺ ions left in the 2p state to He⁺ ions left in the 2s state is in good agreement with recent experiments of Woodruff and Samson (1982), and is consistent with recent experiments of Bizau et al. (1982) there is a serious disagreement with the many-body theory of Chang (1980) close to threshold.