Dispersion relation and volume integrals of optical potential for light projectiles

At low energies the determination of real optical potential is subject to several ambiguities. The dispersion relation involving an integral over the whole domain of imaginary part can then be used in the present note to obtain the correct real volume integral at low energies. Usually the subtracted dispersion relation is utilized by normalizing the real potential at higher energies where the dispersion correction is assumed to be zero, however, this procedure is not entirely satisfactory as all the energy dependence of the real part arises totally due to the dispersion correction at all other energies