One- and two-electron capture in collisions of slowB4+andBe4+ions with helium

One-electron and two-electron capture in slow ${\mathrm{B}}^{4+}$-He and ${\mathrm{Be}}^{4+}$-He collisions are studied within the semiclassical close-coupling description with two-electron atomic basis sets. For ${\mathrm{B}}^{4+}$-He collisions, we find large two-electron capture cross sections to 2l2l’ doubly excited projectile states. Double-capture cross sections to 2${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$ ${\mathit{S}}^{\mathit{e}}$, 2s2p ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}^{\mathit{o}}$, and 2${\mathit{p}}^2$ ${}_{}{}^1{}_{}{}^{}$ ${\mathit{D}}^{\mathit{e}}$ states and the relative M distributions are found to be in good agreement with recent experiments. Earlier data on ${\mathrm{B}}^{3+}$ production are found to contain large portions of double transfer followed by autoionization. For the ${\mathrm{Be}}^{4+}$-He system, the summed cross sections from this work agree with an earlier theoretical study within the adiabatic model. Discrepancies remain, however, for this system in the distribution of double transfer over final states.