One- and Two-K-shell Vacancy Production in Atomic Li by 95-Mev/uar18+projectiles

Singly and doubly K-shell-vacant states in atomic Li, produced by 95-MeV/u Ar18+ projectiles, have been investigated. At this high velocity, excitation and ionization are expected to be well described by perturbation theories. High-resolution spectra for Auger electron emission, occurring in the energy range similar to 50-90 eV and resulting from the deexcitation of singly or doubly excited states, were measured for various electron emission angles. Both single-K-shell excitation and double-K-shell vacancy production show strong dependences on the electron emission angle. Experimental anisotropy parameters for the P-2 states resulting from single-it-shell excitation are in good agreement with predictions of the Born approximation. In the case of double-K-shell-vacancy (i.e., hollow atom) production, the two it vacancies are found to come about mainly by ionization plus excitation of the atomic Li target giving rise to excited states in Li+. Strong line intensities from the 2s(2) S-1 and 2s3s S-3 excited-state configurations are explained in terms of shake processes, providing direct spectral identification for the electron-electron (e-e) interaction in producing the doubly vacant it-shell configurations. Production of the 2s3s S-3 state, which has an intensity greater than that of the 2s(2) S-1 state, is attributed to a three-electron transition involving two shake transitions. Production of the 2s2p P-3 scare has a large contribution from the dielectronic manifestation of the e-e interaction resulting from slow electron emission.