Dynamics of post-collision interaction in the near-threshold electron excitation of the (3p54s2)2P3/2,1/2 autoionizing states in potassium

The post-collision interaction (PCI) energy shift of lines corresponding to the decay of the (3p(5)4s(2))P-2(3/2,1/2) lowest autoionizing states in potassium atoms was studied by precisely measuring the ejected-electron spectra in the excess energy range between 0 and 3.5 eV. The energy dependence of the line shift for both states reveals a complicated character. In particular, instead of the smooth asymptotic behaviour predicted by available models of PCI, the shift can possess both positive and negative sign in an excess energy region between 0.2 and 1.3 eV. Comparison of these data with the near-threshold excitation cross sections of the (3p(5)4s(2))P-2(3/2,1/2) states showed that such behaviour is observed in the same energy regions where the negative-ion resonance structure is present in excitation functions. To explain the observed features, the effect of core-polarization on the final energy distribution of outgoing electrons is considered and the possibility of the negative line shift for the P-2(3/2) and P-2(1/2) states is shown by numerical evaluation.