The post-collision interaction effect in autoionizing spectra of alkali atoms excited by electron impact

Abstract

Ejected-electron energy spectra resulting from decay of the (4p55s2)2P3/2, 1/2 autoionizing states in rubidium atoms have been studied at electron impact energies up to 5 eV above the excitation thresholds. The energy shift of corresponding lines due to the post-collision interaction (PCI) involving the outgoing electrons and the residual ion have been observed for the first time. For both states the energy dependence of the shift possesses a smooth asymptotic behaviour which is satisfactorily described by the classical model of the PCI effect. Similar behaviour of the line shift was reported earlier also for the (5p56s2)2P3/2 autoionizing state in heavier Cs atoms. Both results contrast with the clear oscillatory-like character of the line shift for the (np5[n + 1]s2)2P3/2, 1/2 autoionizing states in the lighter Na (n = 2) and K (n = 3) atoms. The comparative analysis of the data on the PCI effect and excitation cross-sections of the (np5[n + 1]s2)2P3/2, 1/2 autoionizing states in Na (n = 2), K (n = 3), Rb (n = 4) and Cs (n = 5) atoms has shown that the high polarizability of the resonantly excited target and partial structure of resonances are the main factors which determine the dynamics of the PCI shift of lines in ejected-electron spectra of alkali atoms.