We present a combined theoretical and experimental study of primary and postcollision mechanisms involved when colliding low-energy multiply charged ions with van der Waals dimers. The collision dynamics is investigated using a classical calculation based on the Coulombic Over-the-Barrier Model adapted to rare gas dimer targets. Despite its simplicity, the model predictions are found in very good agreement with experimental results obtained using COLd Target Recoil Ion Momentum Spectroscopy, both for the relative yields of the different relaxation processes and for the associated transverse momentum exchange distributions between the projectile and the target. This agreement shows to what extent van der Waals dimers can be assimilated to independent atoms.

Fragmentation of molecular nitrogen dimers (N_{2})_{2} induced by collision with low energy 90 keV Ar^{9+} ions is studied to evidence the influence of a molecular environment on the fragmentation dynamics of N_{2} cations. Following the capture of three or four electrons from the dimer, the three-body N_{2}^{+}+N^{m+}+N^{n+} [with (m,n)=(1,1) or (1, 2)] fragmentation channels provide clean experimental cases where molecular fragmentation may occur in the presence of a neighbor molecular cation. The effect of the environment on the fragmentation dynamics within the dimer is investigated through the comparison of the kinetic energy release (KER) spectra for these three-body channels and for isolated N_{2}^{(m+n)+} monomer cations. The corresponding KER spectra exhibit energy shifts of the order of 10 eV, attributed to the deformation of the N^{m+}+N^{n+} potential energy curves in the presence of the neighboring N_{2}^{+} cation. The KER structures remain unchanged, indicating that the primary collision process is not significantly affected by the presence of a neighbor molecule.