Alignment of He- and H-likePstates of 48-MeV foil-excited Mg ions

The angular distributions of the ${}_{}{}^1{}_{}{}^{}\mathrm{P}$, ${}_{}{}^3{}_{}{}^{}\mathrm{P}$, and ${}_{}{}^2{}_{}{}^{}\mathrm{P}$ lines of 2-MeV/amu Mg projectiles excited by collision with carbon and aluminum atoms in thin foils have been measured with a pivoted plane-crystal Bragg spectrometer. Both the polarizations of these lines and the reflection properties of the ammonium dihydrogen phosphate (ADP) diffraction crystal have been determined. The ${\sigma }_0$/${\sigma }_1$ cross-section ratios for populating the 2p(‖m‖=0) and 2p(‖m‖=1) states in the 1s2p He-like and the 2p H-like configurations were deduced from the polarization values and compared with the coupled-states calculation of Reading et al., assuming that the mechanism populating these states is the capture of electrons from the K shell of the target. The agreement between theory and experiment is very good for carbon excitation, but for aluminum excitation the theory significantly overestimates the cross-section ratio. The influence of foil tilting and cascade contributions on the polarization were investigated experimentally and taken into account in the analysis of the measurements.