Multielectron excitations in x-ray absorption spectra of Rb and Kr

In the K-edge x-ray absorption of rubidium vapour and gaseous krypton, comprehensive spectra of collective excitations down to the relative probability of 5 x 10(-5) are extracted. After removal of the asymptotic Victoreen trend, the region similar to100 eV above the edge exhibits a steep decrease of the absorption coefficient attributed to core relaxation and post-collision interaction in the Auger decay. With an exponential model for the decrease, the entire spectrum of multielectron excitations is recognized as a succession of consecutive resonant, shake-up and shake-off channels. They can be identified as coexcitations of electrons from successively deeper subshells, from 5s down to 3s. The identification of excited states is aided by a quantitative modelling of subshell contributions and by natural-width deconvolution. The valence and subvalence coexcitations are shown to follow the pattern of the lighter homologues potassium and argon.