Ultrafast Dissociation of Metastable CO^{2+} in a Dimer.

We triply ionize the van der Waals bound carbon monoxide dimer with intense ultrashort pulses and study the breakup channel (CO)_{2}^{3+}→C^{+}+O^{+}+CO^{+}. The fragments are recorded in a cold target recoil ion momentum spectrometer. We observe a fast CO^{2+} dissociation channel in the dimer, which does not exist for the monomer. We found that a nearby charge breaks the symmetry of a X^{3}Π state of CO^{2+} and induces an avoided crossing that allows a fast dissociation. Calculation on the full dimer complex shows the coupling of different charge states, as predicted from excimer theory, gives rise to electronic state components not present in the monomer, thereby enabling fast dissociation with higher kinetic energy release. These results demonstrate that the electronic structure of molecular cluster complexes can give rise to dynamics that is qualitatively different from that observed in the component monomers.