Controlling Molecular Fragmentation: Charge Transfer in a Dissociating Molecule*

We investigate control of molecular fragmentation in the halogen-substituted acetone CHBr$_2$COCF$_3$. Feedback experiments can successfully control the CF$_3^+$/CHBr$_2^+$ branching ratio during dissoctiative ionization. Optimal pulse shapes, combined with pump-probe spectroscopy, suggest a control mechanism that transfers electronic charge from the CF$_3$ to the CHBr$_2$ fragment during dissociation. Further tests show that the charge transfer process may be interpreted in terms of adiabatic rapid passage mediated by a dynamic resonance between different electronic states in the dissociating molecule. This control mechanism provides a possibility for measuring the nuclear wave function of the dissociating molecule.