Experimental study of Penning and Hornbeck-Molnar ionisation of rubidium atoms excited in a high s or d level (5d⩽nl⩽11s)

Abstract

Rb+ and Rb2+ formation in a laser-excited Rb vapour is extensively studied for s and d levels ranging from 5d to 11s levels. Collisional ionisation with a ground-state atom leads to Rb2+ formation by Hornbeck-Molnar reaction with rate coefficients lying in the 10-10 cm3 s-1 range. This reaction is analysed theoretically. Penning ionisation occurs in collision with a resonant-state atom, Rb(5p), with a high efficiency (rate coefficient above 10-8 cm3 s-1). Associative ionisation between the 7s level and the 5p level is also observed (rate coefficient about 10-10 cm3 s-1). This reaction appears negligible for the neighbouring 5d level.