The refractive index data for Zn and Cd measured by Goebel and Hohm are analyzed with a three-term Maxwell-Sellmeier expression which incorporates the experimental oscillator strengths of the first two dipole transitions. These expressions are extended to imaginary frequencies for the determination of the upper and lower bounds of the dynamic polarizabilities α(iω), from which the van der Waals coefficients of two-body interactions and the non-additive three-body interactions are generated. The determined C(6) values for Zn(2) (359±8 a.u.) and Cd(2) (686±10 a.u.) are much larger than those originally estimated by Goebel and Hohm. This is because their one-term approximation of α(ω), which fits the measurements very well in the normal frequency range, greatly underestimates α(iω) when the frequency is extended into the imaginary domain. On the other hand, the present results of heteronuclear interactions verify once again that Tang's one-term approximation of α(iω) leads to accurate combining rules. The two- and three-body interaction coefficients between group 12 atoms (Zn, Cd, Hg) and the alkali, alkaline-earth, rare-gas atoms, and some molecules are estimated with these combining rules.