H-2-B-(1)SIGMA(-FIELD()(U) PHOTODISSOCIATION IN AN INTENSE INFRARED LIGHT)

The first experiment on 1064 nm infrared (IR) multiphoton excitation o f H-2 with single B-1 Sigma(u)(+)(upsilon = 3.J) rotational levels as initial states is reported. These states are prepared by one-photon ex citation from the molecular ground state. We investigate the H-2(+) an d H+ ion yield, the dissociation fraction H+/(H-2(+) + H+) and the Hion kinetic energy distribution as a function of the IR light intensit y in the range from 5 x 10(9) W cm(-2) up to 7 x 10(11) W cm(-2). The dissociation fraction depends sensitively on the initial rotational st ate. Transient resonances induced by AC Stark shifting states seem to influence the branching ratio between photoionization and dissociation . The H+ photoion kinetic energy distributions show that the molecule dissociates after three-photon absorption into H(1s) + H(2l). The H(2l ) atoms are then photoionized. The AC Stark shift of the final dissoci ation product states H(2l) in the IR light field seems to be responsib le for a small intensity-dependent shift of the H+ kinetic energy dist ribution.