Emitted electron spectra from doubly-excited states 1s(2)nln'l' of Be-like ions produced by the collisions of O6+ and C4+ ions with alkaline-earth atoms

Electron spectra ejected from doubly excited states of Be-like ions produced by two electron capture processes in O6+ + Ca, C4+ + Mg and C4+ + Ca collisions have been measured by means of high resolution zero-degree electron spectroscopy. For the O6+ + Ca collision, spectra from the 1s(2)4lnl' and 1s(2)5lnl' states are observed in addition to those from the 1s(2)3lnl' states in which n equals six or larger. For the C4+ + Mg and Ca collisions, spectra from the 1s(2)3lnl' and 1s(2)4lnl' states are observed Population distributions of the states are explained as a whole using the concept of the reaction window based on the extended classical over-barrier model by Niehaus.