Dissociative ATI of H2 and D2 in intense soft x-ray laser fields

The dissociative photoionization processes of H-2 and D-2 in an intense, short-pulsed soft x-ray field (lambda = 29.6 nm, 3 x 10(12) W CM-2, 15 fs) generated as the 27th high-order harmonic of a Ti:sapphire laser is investigated for the first time by time-of-flight mass spectrometry. The ejected H+ fragment ions from H2 are distributed in the kinetic energy range of 3-20 eV peaked at 10.0 eV, and the yield exhibits a nonlinear dependence of the order of 1.7(l) on the light field intensity of the 27th harmonic. Similarly, the D+ fragment ions from D-2 are distributed in the 3-20 eV range peaked at 10.3 eV, and the yield exhibits a nonlinear dependence of the order of 1.6 +/- 0.2. The kinetic energy distributions of H+ and D+ and the nonlinearity in their yields are interpreted well by the two coexisting ionization processes: (i) one-photon dissociative ionization and (ii) dissociative two-photon above-threshold-ionization (ATI) mainly into the repulsive 2p pi(u) state.