Resonant double excitation observed in the near-threshold evolution of the photoexcited F K alpha satellite intensity in NaF

We present a precise measurement of the photoexcited F K alpha satellite intensity's evolution for NaF from 1s2p] double excitation threshold to saturation. A direct comparison between the observed evolution and the x-ray absorption spectrum was successfully made, and the contribution of multielectron transitions to the absorption spectrum was clearly resolved for the first time. A resonance-like feature observed in the near-threshold evolution is attributed to the 1s2p]3p(2) resonant double excitation as confirmed by calculations.