OBSERVATIONS OF DOUBLY-EXCITED STATES IN LITHIUM-LIKE CALCIUM

We report observations of simultaneous electron excitation and electro n capture in ion-atom collisions of 97-MeV Ca18+ and Ca19+ in an argon gas target. X-ray spectra at energies near 3.9 keV were collected usi ng a high-resolution x-ray spectrometer. We have resolved transitions from doubly excited 1s2l2l' and 1s2l3l' states to singly excited 1s(2) 2l' and 1s(2)3l' states in lithiumlike calcium. The observed transitio ns lie at energies close to the 1s2s-1s2p resonance transitions in hel iumlike calcium. We compare the experimental wavelengths and intensiti es with relativistic Hartree-Fock calculations, and discuss the excita tion mechanisms.