Resonant multiphoton ionisation-dissociation of H2

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Abstract
The authors have studied the five-photon ionisation of H2 via the four-photon resonance on the E, F1 Sigma g+, vE=2 from X1 Sigma g+, v=0 transition. A dye laser delivering up to 5*1011 W cm-2 around 3860 AA is focused into an H2 cell at room temperature and at a pressure of 5*10-4 Torr. The time-of-flight mass spectrum exhibits comparable signals of H+ and H2+ thus demonstrating the existence of an important dissociative mechanism superimposed on the ionisation channel. Different processes are considered to tentatively explain this unexpectedly high probability of the multiphoton dissociation of H2.