CALCULATED CROSS-SECTIONS FOR THE DOUBLE-EXCITATION OF HELIUM BY CHARGED-PARTICLE IMPACT

After the recent work of Moretto-Capelle et al (1997 Phys. Rev. Lett. 76 5230) the direct comparison of the theoretical double-excitation cr oss sections with experiment became possible. Cross sections for the e xcitation of the (2s(2))S-1, (2s2p)P-1 and (2p(2))D-1 states of helium are calculated for proton and antiproton projectiles over a wide impa ct energy range. Our results are in good agreement with the experiment al data. The dependence of the cross sections on the sign of the proje ctile charge, the importance of the different mechanisms causing the t wo-electron transitions and the obtained magnetic sublevel populations are also analysed.