Split window resonances for the photoionization of spin–orbit coupled subshell states in alkali atoms

Abstract

We study the origin of dual window-type 3 s → 4 p photoexcitation resonances of potassium atoms that have been observed previously [M. Koide et al., J. Phys. Soc. Jpn. 71 (2002) 1676] by means of photoion spectroscopy. We also consider the sub-valence shell photoexcitations of other alkali metal atoms. In potassium 3p photoionizations, the photoion energy levels may be labeled by their total angular momenta, and they are well separated due to the spin–orbit couplings in 3p subshells. The system of a photoion and a photoelectron is therefore a superposition of different total spin states if expressed in terms of the LS-coupling scheme. The ionization continuum may couple with several intermediate discrete states with different total spin quantum numbers, giving a possibility to observe split resonance structures in the spectra of 3 s → n p photoexcitations and in other alkali-atom photoexcitations. We discuss the dual window-type resonances in potassium, rubidium, and cesium atoms.