We present studies on collision induced dissociation of C₂⁻ with Ar at an impact energy of 15 keV. The C⁻ fragment ion kinetic-energy release (KER ) distribution is measured and is used to compute the KER in the center of mass (c.m.) frame (KER_c.m.). We employ the reflection method to deduce an effective repulsive potential-energy curve for the molecular anion that is otherwise difficult to evaluate from quantum computa-tional methods. The nuclear wave packet of the molecular ion in the initial ground state is computed by the semiclassical WKB method using the potential-energy curve of the ²Σ_g⁺ ground electronic state calculated by an ab initio quantum computation method. The ground-state nuclear wave packet is reflected on a parametrized repulsive potential-energy curve where the parameters are determined by fitting the measured KER_c.m. with the calculated KER distribution.