Abstract
The authors have studied the two-photon ionisation of the E, v=0, J=0 metastable state of H2 with resonance on the 4p pi 1 Pi +u, v=1, J=1 level, in the 104-109 W cm-2 laser intensity range. Anomalous dips are observed at resonance (4777.5 AA) on the ionisation signals. These dips are due to competition of photoionisation with very fast predissociation. The resonance profiles exhibit a strong power broadening (55 cm-1 GW-1 cm2) due to photoionisation of the resonant level whose cross section is measured to be (7+or-2)*10-16 cm2.