Excitation of the ${3p}^4\mathrm{}(4s,3d,4p)\mathrm{}$ ${\mathrm{Ar}}^{+}$ states during Ar photoionization: Intensity, alignment, and orientation

Ar photoionization is studied using the R-matrix formalism with emphasis on the simultaneous excitation of the residual ${\mathrm{Ar}}^{+}$ ion. Cross sections have been obtained for excitation of the ${3p}^4\mathrm{}(3d,4s,4p)\mathrm{}$ states. A comparison with experiments having a resolution of 70 meV shows reasonable agreement for the position and shape of resonance structures. The relative magnitude of the resonances proves to be more elusive. The partial cross section for excitation of the ${3p}^4{(}^3{P}^e)4p{}^2{P}_{3/2}^o$ and ${}^2{D}_{3/2}^o$ levels is treated in more detail. A comparison of $\mathrm{LS}$-coupling calculations with high-resolution experimental results shows good agreement for both the excitation cross sections and the polarization of the fluorescence. We also predict the orientation for both levels. We demonstrate that the polarization of the fluorescence originating from the ${}^2{D}_{3/2}^o$ level can be employed to study spin-orbit effects in Ar photoionization.