Dynamics of electron excitation of low-energy quartet states of the potassium atom

The electron excitation function for the lowest (3p ⁵3d4s)⁴ P autoionizing quartet level of the potassium atom is measured in the energy range from the threshold of the process to 102 eV at the energy resolution of 0.3 eV or better. The near-threshold energy region is studied in detail for the first time. The main processes that govern the dynamics of excitation of the low-lying quartet levels in the potassium atom are analyzed by comparing these data with the excitation functions obtained earlier for the (3p ⁵4s4p)⁴ S and (3p ⁵4s4p)⁴ D levels. In particular, the resonances of negative ions in the near-threshold energy region are shown to play a dominant role, as well as to significantly affect the efficiency of the cascade transitions from higher-lying quartet levels.