State-selective double-electron capture in low-velocity collisions studied by recoil-ion momentum spectroscopy

Abstract

State-selective double-electron capture from He by a fully stripped 150 keV projectile is investigated by recoil-ion momentum spectroscopy (RIMS). For each event, identified by the projectile and recoil-ion final charge states, the full recoil-ion momentum vector allows the determination of the Q-value and the scattering angle simultaneously, thus leading to doubly differential cross sections for each channel. This collision system has already been studied by energy gain, electron and photon spectroscopy as well as theoretically. A large fraction of the doubly excited states populated were found to be non- or weakly autoionizing. In this paper all channels are recorded together so that a detailed balance between channels can be discussed and compared with existing data. Special emphasis is brought to the analysis of the angular behaviour to highlight the population mechanism for the channels contributing to the `double-capture stabilization'. In particular, a new pathway leading to transfer excitation channels in double capture is proposed.