Resonance excitation of the 3p6-subshell in potassium. Contribution to the single ionization

Full text: It is well known, that autoionization processes play important role in electron impact ionization of heavy metal atoms [1]. Recent high-resolution studies of the near-threshold ionization for Zn and Cd atoms revealed the significant role of resonance processes [2]. In the case of potassium atoms, the rapid rise of the single ionization cross-section in a region close to the 3p6- excitation threshold could reflect also an influence of resonance excitation of autoionizing states [1]. For the purpose of examining this assumption, the investigations of ejected-electron excitation functions for the most low-lying 3p54s22P1/2,3/2 and 3p53d4s 4Pj, 4Dj autoionizing levels have been performed with an energy resolution of 0.25 eV. The ejected-electron spectrometer and the method for obtaining the ejected-electron excitation functions both have been described elsewhere [3]. The spectra of ejected-electrons have been measured at an observation angle of 54.7 deg in an electronimpact energy range from the excitation thresholds of levels up to 500 eV. The main feature of the data is the presence in excitation functions of the strong and well-resolved resonant structure just above the excitation thresholds of levels. The resonance part of the excitation cross-section for the 2P1/2,3/2 and 4Pj levels exceeds 1.5/3.5 times the maximum value of the cross-section for the direct excitation process. For the 4Dj level both cross-sections are comparable by magnitude. The identification of resonances shows that their origin could relate to the electron decay of the shape- and negative-ion resonances formed upon p5s2 and p5ds configurations. Basing on these data, one could confirm that at the impact energies close to the excitation thresholds of these configurations the single ionization cross-section is essentially affected by the resonance excitation of autoionizing levels. The complex analysis of the results together with a quantitative evaluation of the resonance- and direct ionization cross-sections will be presented at the workshop