Observation of a collective excitation in the ejected-electron spectra of Yb and Ba

Ejected-electron spectra of Yb and Ba are presented. In both spectra, structure was seen which is attributable to autoionization to ground and excited states of M⁺ (M=BaorYb), and to Auger decay of highly excited M*+ states to the ground state of M²⁺. In Yb, Auger decay was also observed to populate excited states of M²⁺. Both spectra are strongly affected by a collective resonance in the excitation of a $5p$ electron. For energies above the $5p$ ionization threshold, two-step autoionization to M²⁺ was found to be dominant.