Alignment And Dissociation Of Electronically Excited Molecular Hydrogen With Intense Laser Fields

The dissociation of aligned, electronically excited H2 (E,F (1)Sigma(g+)), followed by the ionisation of the produced H atom, is analysed via the velocity mapped imaging technique. The dissociation and ionisation processes are accomplished, respectively, by a two- and a one-photon absorption from a single 532-nm laser pulse, while the alignment is induced by a separate 1064-nm laser pulse. The velocity of the produced H+ photofragments shows a weak perpendicular alignment at low align-ment laser field values, evolving to strongly parallel for larger fields. We modelled this alignment behaviour with a simple two-state model involving the Stark mixing of the initially-prepared J = 0 with the) = 2 rotational state. This model is able to reproduce all of the observed angular distribution and permits us to extract from the fit the polarisability anisotropy of H-2 (E,F) electronic state. We determine this value to be (3.7 +/- 1.2) x 10(3) a.u. As this value is extremely large in comparison to what one would expect from the pure H-2 (E,F) electronic state, we hypothesise that this value comes from the 1064-nm laser beam mixing nearby electronic states with the initially laser prepared (E,F) state generating a mixed state (EF**) with an extremely large polarisability anisotropy.[GRAPHICS].