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

We have determined photoionization spectra of Ar with excitation of the 3p( 4)(P-3)4p states emphasizing the effects of two different classes of Ar+ sp in-orbit interactions. The spin-orbit splitting of each Ar+ state adequatel y describes the resonant excitation of the quartet states of Ar+, and gives Ar photoionization cross sections with excitation of the 3p4(3P)4p P-2(3/2 )o and P-4(5/2)o levels of Ar+ in sufficiently good agreement with experime nt to identify the observed resonances and to estimate the excitation stren gths. In addition, we demonstrate the importance of spin-orbit induced mixi ng of different Ar+ LS-coupled states for observables such as the alignment of the 3p(4)(P-3)4p P-4(5/2)o level and the excitation of Rydberg series c onverging to the 3p(4)(P-3)4p S-2(o) and S-4(o) thresholds.