Treating isotopically substituted molecule as a perturbed system, Grees’s function for the perturbation are constructed and related to the force field of vibration. By spectral representation, Green's function is diagonalized in the normal coordinates. Then transforming back to the Cartesian coordinates, the Cartesian force constants are generated without solving the secular equation directly. The relations between the internal force constants and the Cartesian force constants are given and complete internal forve field can be obtained. The results for H2O are discussed.
中國化學會會誌=Journal of the Chinese Chemical Society 19(2)，頁49-56