Collisional processes of [Formula: see text] with a silicon surface were investigated. Size-selected [Formula: see text](n=0–30) were allowed to collide with a silicon surface at collision energies per [Formula: see text] of 1–150 eV at almost normal incidence angles. All the anions scattered from the surface were I −, I −( CO 2), I −( CO 2)2, [Formula: see text], [Formula: see text], and [Formula: see text]. The molecular dynamics simulation revealed that the dissociation of [Formula: see text] occurs through vibrational and rotational excitation. The [Formula: see text] dissociation was found to be either retarded or accelerated by the presence of the solvent CO 2 molecules. The solvation effects on the dissociation of [Formula: see text] were explained in terms of energy transfer between [Formula: see text] and CO 2 solvent molecules and a complex formed on the surface at the moment of the collision.