Electron-impact excitation of potassium autoionizing levels in the near-threshold region

The metastable excitation function and the near-threshold energy loss spectrum in potassium, corresponding to 3p6 core excitation, have been measured over the energy range 18-24 eV. Many structures have been observed for the first time in the metastable excitation function. From a comparison of the observed yields of metastable atoms and scattered electrons, various processes for metastable production are considered, including resonance excitation and radiative cascade. The excitation thresholds for the lowest-lying metastable autoionizing levels in potassium, namely 3p54s4p 4D7/2 and 3p53d4s 4F9/2, have been determined to be 20.28?0.05 eV and 20.42?0.05 eV, respectively.