Autoionization Cross Section of Lithium Atoms Excited by Electron Impact

摘要

We measure the full autoionization cross section of lithium atoms excited by electrons in the energy range from the first autoionization threshold at 56.39 to 600 eV. Data are obtained by determining the total intensity of electron spectrum of autoionization states 1sn_(1)l_(1)n_(2)l_(2) detected at the "magic" observation angle of 54.7 deg. The cross section behavior is characterized by a sharp increase to a maximum value of 1.7 X 10~(-18) cm~(2) in the energy interval of 56.4-60 eV and a subsequent monotonic drop to a value of 10~(-18) cm~(2) at 600 eV. We have discovered a "thin" cross section structure that reflects the presence of strong resonances of Li~(-) ions in the near-threshold area of excitation of the lowest energy autoionization states (1s2s~(2))~(2)S, (1s2s2p)~(4)P, 1s(2s2p~(3)P)~(2)P), and 1s(2s2p~(1)P)~(2)P. We have established that the contribution of autoionization to the absolute cross section of single ionization of lithium atoms does not exceed 4percent. We perform a comparative analysis of the data with analogous data for potassium and cesium atoms.