Double electron capture by He-like ions: Collision energy dependence of the reaction window

Abstract

Double electron capture by the He-like ions C 4+, N 5+, O 6+, Ne 8+ from the two electron targets H 2 and He is studied by spectroscopy of the autoionization electrons emitted after capture into excited states. Electron spectra are measured in a collision velocity range from 0.18 to 0.55 atomic units. The spectra are found to be due to decay of states of the type (1s 2 3 ln′ l′ and (1s 24 ln′ l′) into the continua (1s 22 l + e and (1s 2 3 l + e. respectively. It is found that only states lying, within a certain reaction window are populated. Energy position and dependence of the width of this window on the collision velocity are discussed and compared with predictions of the classical model for multiple electron capture.