Use of the ac Stark effect to alter the mechanism of formation of doubly charged ions in the ionisation of barium atoms by visible light

The influence of an additional perturbation (the ac Stark effect) of neutral barium atoms on the formation of doubly charged ions in the course of ionisation of these atoms by visible light (by the second harmonic radiation of an yttrium-aluminium garnet laser) was investigated experimentally. The frequency-tunable radiation of a colour-centre laser (ω = 8500 —7 8950 cm^–1 ) was used in these investigations to effect the additional perturbation of barium atoms. It was found that this perturbation changed the mechanism of formation of the doubly charged Ba²⁺ ions from a stepwise to a two-electron mechanism. The yield of the Ba²⁺ ions increased sharply under these conditions.