An approximate method for diffraction analysis of equilibrium geometries of molecules which extensively uses dynamical information from computational sources is developed. The method obviates refinement of the harmonic force field of a molecule by using the eigenvector matrix obtained from mopac semiempirical calculations of the PM-3 type and spectroscopically observed or scaled mopac vibrational frequencies. The frequency scale factors were adjusted in the course of the analysis of diffraction data. A simple account for anharmonicity was also made by the aid of the Morse oscillator potential function. The method was checked against analysis of diffraction data for the sample molecules CO 2 , SO 2 and SF 6 .