TRANSFER EXCITATION IN SLOW COLLISIONS BETWEEN IONS OF VERY HIGH CHARGE AND 2-ELECTRON TARGETS

We argue that a three-step transfer-excitation (capture and target excitation) mechanism enhances (depletes) the cross section for one- (two-) electron removal from a two-electron target. This mechanism, which becomes very important at high projectile charge (q), is mediated through quasimolecular couplings between diabatic double-capture and transfer-excitation channels, in which the inner of two active electrons is transferred to an excited target state. The inclusion of this process in the extended classical over-barrier model gives excellent agreement with unexplained experimental cross sections for one- and two-electron removal from He is slow collisions with Xe ions of high charge (q less-than-or-equal-to 31).