Energy-dependentKLdouble photoexcitation of argon

The fluorescence KL x-ray emission of argon induced by impact with monoenergetic photons was observed with a high-resolution reflecting-type bent crystal spectrometer. The measurements were performed at the European Synchrotron Radiation Facility in Grenoble, France. X-ray beam energies in the range 3455 eV<~ω<~6540 eV were used to investigate the $K+L$ double excitation from threshold to saturation. The excitation probabilities were deduced from the satellite-to-diagram line yield ratios I(KL-L2,3L): I(K-L2,3). Results were compared to predictions based on the model of Thomas and the one of Roy. From the comparison, parameters such as excitation onset energies, high-energy limit shake probabilities, and radius of the $2p$ orbital in ionic Ar were deduced. The satellite line shapes and their evolution with the excitation energy were analyzed with the aid of multiconfiguration Dirac-Fock calculations.