Experimental investigations of two-electron relaxation processes in Rydberg hollow atoms

The two-electron relaxation processes in Rydberg hollow atoms (RHA), formed in collisions of slow highly charged ions (HCI) of Xeq+ (q = 23-36) with metallic Be surface, were studied experimentally by means of X-ray spectroscopy. The pulsed beams of HCI were delivered by the electron beam ion source while the emitted X-rays were observed by a silicon drift detector. From the measured spectra of M-X-rays, dominated by the Paschen series of nf -> 3d one-electron-one photon radiative (R) transitions, the relaxation processes involving two electrons, namely, the internal dielectronic excitation, interatomic Coulombic decay, two-electron-one photon transitions and the Auger transition (A), were extracted. The dead-time effect in X-ray detector for a pulsed ion beam of HCI was considered in order to estimate the Auger decay rates. Finally, we demonstrate that the present results give access to estimate a time-scale of relaxation of RHA in solids.