Excitation of the 3p54s22P autoionizing state in potassium by electron impact at low energies: anR-matrix calculation

An R -matrix method is applied for extensive calculations of the excitation cross section for the 3p 5 4s 2 2 P autoionizing state in potassium by electron impact at incident energies between threshold (18.7 eV) and 31 eV. Up to 134 atomic states are included in the close-coupling expansion. The cross section is dominated by a strong negative-ion 3p 5 3d4s 2 3 F o resonance just above the excitation threshold. The results are compared with recent experimental data.