L-shell Auger electron generation across the Kr K-edge

We have used high-resolution electron spectroscopy at the Advanced Photon Source to study resonance and threshold variations of the 1611-eV L₂-M_4,5N_2,3 Auger line as the x-ray energy is scanned across the 14327.2-eV Kr K-edge.  X-ray absorption excites the Kr 1s-np Rydberg series below threshold and the 1s continuum above threshold.  The Auger line is only weakly generated by direct L₂ photoionization and strongly enhanced by K-L₂ x-ray emission.  Consequently, the yield of the L₂ Auger electron follows the K-edge absorption cross-section, including the 1s-np Rydberg states, resulting in resonant Auger lines.  Above threshold, small energy shifts of the Auger line result from post-collision-interaction (PCI) with 1s photoelectrons.  Due to the 2p-1s fluorescence time delay [1], modeling PCI effects requires combining the 0.24-fs 1s lifetime with the 0.50-fs 2p_1/2 lifetime. The results demonstrate the sensitivity of high-resolution electron spectroscopy combined with synchrotron x rays for inner-shell studies of heavy atoms.