Laser photodissociation of Na2+ions produced by laser resonant and non-resonant ionisation of Na vapour

Abstract

The authors report direct measurements of the photodissociation of Na2+ ions created when a Na vapour in the density range 1012-1013 cm-3 is irradiated by a pulsed laser with intensities in the 105-106 W cm-2 range. The Na2+ ions, accelerated by a weak electric field, are photodissociated in a second laser beam tuned to 6040 AA. In a preliminary experiment the Na2+ ions are formed in the lowest vibrational levels and the measured photodissociation cross section is compared with existing calculations. When the Na vapour is irradiated at one of the 3S1/2-3P1/2,3/2 resonances the photodissociation measurements show the existence of a distribution of rovibrational excited levels of the Na2+ ions. A discussion is given in terms of associative ionisation in collisions of two Na(3p) atoms. The origin of the Na+ ions produced simultaneously with the Na2+ ions, in the vapour irradiated at resonance, is also discussed.