Six-photon ionisation of H2via the E, F,1Σg+, νE=0 level. Absorption of photons in the ionisation continuum

Abstract
The authors have observed the six-photon ionisation of H2 with four-photon resonances on the E, F 1 Sigma g+, nu E=0 levels, using laser intensities in the range of 1011 W cm-2 and photon energies around 3.07 eV. Contrary to all expectations, there is evidence for significant H+ production; both H+ and H2+ ion resonance spectra are dominated by the Q lines of the four-photon transitions E, nu E=0 from X, nu =0. From the electron energy spectra, which show a strong nonFranck-Condon behaviour, it appears that the H+ ions are formed by photodissociation of H2+ ( nu +=2). At higher intensity (1012 W cm-2) the authors demonstrate the absorption of two extra photons by the H2 molecule into the X 2 Sigma g+ ionisation continuum.

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