K -edge x-ray absorption spectra of Cs and Xe

X-ray absorption spectrum of cesium vapor in the K-edge region is measured in a stainless steel cell. The spectrum is free of the x-ray absorption fine structure signal and shows small features analogous to those in the spectrum of the neighbor noble gas Xe. Although the large natural width of the K vacancy (>10eV) washes out most of the details, fingerprints of multielectron excitations can be recognized at energies close to Dirac-Fock estimates of doubly excited states $1s4(d,p,s)$ and $1s3(d,p).$ Among these, the $1s3p$ excitation 1000 eV above the K edge in both spectra is the deepest double excitation observed so far. Within the K-edge profile, some resolution is recovered with numerical deconvolution of the spectra, revealing the coexcitation of the $5(p,s)$ electrons, and even the valence $6s$ electron in Cs. As in homologue elements, three-electron excitations, either as separate channels or as configuration admixtures are required to explain some spectral features in detail.