  The fragmentation of carbon monoxide dimers induced by collisions with low
energy Ar$^{9+}$ ions is investigated using the COLTRIMS technique. The
presence of a neighbor molecule in the dimer serves here as a diagnostic tool
to probe the lifetimes of the $\rm CO^{2+}$ molecular dications resulting from
the collision. The existence of metastable states with lifetimes ranging from
2~ps to 200~ns is clearly evidenced experimentally through a sequential 3-body
fragmentation of the dimer, whereas fast dissociation channels are observed in
a so-called concerted 3-body fragmentation process. The fast fragmentation
process leads to a kinetic energy release distribution also observed in
collisions with monomer CO targets. This is found in contradiction with the
conclusions of a former study attributing this fast process to the perturbation
induced by the neighbor molecular ion.
