A NEW MECHANISM FOR POPULATING EXCITED-STATES OF LI-LIKE IONS

Recent laboratory experiments by Caldwell and co-workers have shown that the radiationless decay of Be (1s2s2np 1P0) is more likely to populate an excited level of Be+ than the ground state. In view of the possible astrophysical importance of this process we have carried out calculations to ascertain whether it applies to beryllium-like carbon and oxygen ions. Our theoretical Auger rates for producing lithium-like carbon and oxygen in the 2s, 2p, and 3p states after autoionisation of C2+ and O4+ follow a similar pattern to the experimental ones for Be and we conclude that the dominant decay path for the doubly excited states 1s2s2np (n = 2,3) of Be-like ions, following ejection of an Auger electron, is the one which leaves the residual Li-like ion in an excited 2p or 3p state. An important consequence is that inner-shell excitation of a Be-like ion (or K-shell ionisation of a B-like ion) followed by Auger decay can be an efficient mechanism for populating excited states of lithium-like ions.