Singly and doubly K-shell-vacant states in atomic Li, produced by 95-MeV/u ${\mathrm{Ar}}^{18+}$ 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 ∼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 ${}^{2}P$ states resulting from single-K-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 K vacancies are found to come about mainly by ionization plus excitation of the atomic Li target giving rise to excited states in ${\mathrm{Li}}^{+}.$ Strong line intensities from the ${2s}^2{}^{1}S$ and $2s3s{}^{3}S$ 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 K-shell configurations. Production of the $2s3s{}^{3}S$ state, which has an intensity greater than that of the ${2s}^2{}^{1}S$ state, is attributed to a three-electron transition involving two shake transitions. Production of the $2s2p{}^{3}P$ state has a large contribution from the dielectronic manifestation of the e-e interaction resulting from slow electron emission.

• Received 3 April 2000

DOI:https://doi.org/10.1103/PhysRevA.62.032715