We report ab initio calculations of ${\mathrm{H}}_2$ ionization by $\mathrm{VUV}/\mathrm{fs}$ ${10}^{12}\mathrm{W}/{\mathrm{cm}}^2$ laser pulses including correlation and all electronic and vibrational degrees of freedom (DOF). Inclusion of the nuclear DOF leads to a substantial increase of resonance enhanced multiphoton ionization. By varying pulse duration, it is possible to control the ratio of dissociative to nondissociative ionization as well as the final ${\mathrm{H}}_2^{+}$ vibrational distribution. For pulses longer than 10 fs and $\hslash \omega >0.46\mathrm{a}.\mathrm{u}.$, dissociative ionization entirely dominates, which is a very unusual situation in photoionization studies.

• Received 17 November 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.143001