Energy-dependent KL double 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<~ħω<~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-L_2,3L):  I(K-L_2,3). 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.