Spin-orbit effects on photoionization-produced alignment of the Ar+3p4(3P)4p levels

We have determined photoionization spectra of Ar with excitation of the 3p 4 ( 3 P)4p states emphasizing the effects of two different classes of Ar + spin-orbit interactions. The spin-orbit splitting of each Ar + state adequately describes the resonant excitation of the quartet states of Ar + , and gives Ar photoionization cross sections with excitation of the 3p 4 ( 3 P)4p 2 P o 3/2 and 4 P o 5/2 levels of Ar + in sufficiently good agreement with experiment to identify the observed resonances and to estimate the excitation strengths. In addition, we demonstrate the importance of spin-orbit induced mixing of different Ar + LS-coupled states for observables such as the alignment of the 3p 4 ( 3 P)4p 4 P o 5/2 level and the excitation of Rydberg series converging to the 3p 4 ( 3 P)4p 2 S o and 4 S o thresholds.