Abstract
Experimental investigations of resonant structure in doubly charged ion (A2+) formation were carried out during Sr and Ba atom ionization by infrared laser radiation (ω = 8400-9100 cm-1). It has been shown that in this case the mechanism of ion formation is a two-electron process - the ions are produced immediately from the neutral atoms. It has been found for the first time that the resonant structure in A2+ ion formation in such conditions is due to the excitation and ionization of neutral-atom mixed states. The atomic-state mixing in this case results from the Stark effect provided that the polarizability of these states is very high.