Differential ionization of Li(2s) and Li(2p) under proton and O8+impact

Abstract

1.5 MeV/amu on Li(2s) and Li(2p). It is shown that the proton measurements lie very much in the first Born regime and that the comparison is therefore more of a test of the experiment than of the theory which, at the first Born level, is considered to be quite accurate. By contrast, the O 8+ measurements present a nonperturbative scenario which provides a substantive challenge to the full CP theory. Although there are exceptions, the CP approximation generally agrees well with the shape of the O 8+ data but there is a drift in normalization between the calculated and measured cross sections with increasing electron ejection energy. This same drift is seen in comparison between CP and measurements of dσ/dEfrom Fischer et al. [ Phys. Rev. Lett.109, 113202 (2012)]. The convergence of the CP approximation with respect to the angular momenta of the pseudostates and their number is investigated. It is concluded that the 164-state set employed here should be satisfactory. Comparison is also made with the even more recent fully differential (triple differential) measurements of Hubele et al. [Phys. Rev. Lett. 110, 133201 (2013)] for O 8+ impact on Li(2s) and Li(2p) at 1.5 MeV/amu. The CP approximation reproduces the “wings” seen in the Li(2s) measurements, which are due to the interaction between the projectile and target nuclei and the node in the 2s wave function, and the asymmetric shape of the 2p data. The orientational dichroism between the 2p+1 and 2p−1 states is illustrated. Overall, and while not perfect, the agreement between the pseudstate theory and the experiments is very encouraging.