Methods are derived whereby vibrationally inelastic cross sections may be inverted to obtain a spherically symmetric effective potential (a rotational average of the complete potential) for atom/diatomic collisions. Classical and semi-classical methods are used to obtain inelastic opacity and deflection functions; these are further processed to give particular classical functions which can be evaluated using a small number (⪅ 10) of trajectories. These are then fitted by a parametrized potential function. The methods successfully invert cross sections computed from a known potential. Results of an inversion of experimental vibrationally inelastic scattering data for Li+/H2 are also presented.