Single-electron capture in 3-keV/u Ar8+ -He collisions

The electron transfer mechanism was investigated for the single-electron-capture process in 3-keV/u Ar8+ -He collisions with cold target recoil ion momentum spectroscopy. The different state-selective electron capture processes were identified for one 1s electron of He capture into 4s, 4p, 4d-4f, and 5s-5p states of Ar8+. We observed that 1s to 4s capture mainly happens at small transverse recoil ion momentum, while 1s to 4p capture mainly happens at large transverse recoil ion momentum. By comparing the measured projectile scattering angle distributions to the theoretical calculations, it is suggested that 1s to 4s and 1s to 4p state-selective capture processes are mainly caused by radial and rotational coupling effects, respectively, and the 4p +/- 1 quantum states are preferred.