Electric-dipole-momentum sensitive Coulomb explosion in doubly ionized CO dimer and trimer: An environmental effect at molecular-scale

Molecular clusters are aggregates of molecules weakly bound by the van der Waals force between molecules. Removing one electron from each constitutive molecule results in van der Waals bond cleavages through Coulomb explosion. This provides an ideal prototype to further study the environmental effects played by one fragmented ion on the other one at the molecular scale. Here, we report an experimental measurement of the two-body Coulomb explosion of (CO)22+ and (CO)32+, produced in a 40 keV Ar2+ double-electron capture collision with a CO dimer and trimer. Accurate reaction pathways are identified with the advanced ion-ion coincidence and momentum-imaging techniques. The measured kinetic energy release deviates from the calculated results based on the reciprocal of internuclear distance (i.e., Coulomb interaction only) and which, therefore, requires the inclusion of rotational energy of CO+ initiated by molecular electric-dipole momentum. Molecular dynamics simulations reveal that the separation defining the rotational energy takes place within a few hundred fs after the onset of dissociation. This molecular-scale environmental effect significantly brings calculations and measurements of the kinetic energy release into agreement.