Two-electron excitation and autoionisation processes in Na⁺-Ne collisions near threshold energy

Abstract

By means of differential energy-loss measurements, autoionisation processes have been studied mostly at a centre-of-mass collision energy of E=93 eV, around which two-electron excitation due to potential curve crossing begins to arise. Additional experiments were done at E=107 and 163 eV. The velocity of the scattered particles was analysed by a time-of-flight technique. In the energy-loss spectra, two peaks of the autoionised Ne+ ions located at energy losses of Q approximately=45 and 37.5 eV were observed. The former loss peak is attributed to the reaction Na++Ne to Na++Ne(2s22p4(1D)3s2 1D)-45.2 eV Ne++e- and the latter peak can be interpreted in terms of the rainbow effect appearing in the molecular autoionisation process. The two-electron excitation process described above can be well understood as proceeding through two successive one-electron excitation processes Ne(2s22p6) to (Ne(2s22p53s)) to Ne(2s22p43s2).