M. Sugie, M. Kato, C. Matsumura, and H. Takeo
[J. Mol. Struct., Vol.413-414, pp.487-494, 1997]

Microwave spectra of 1,2-dichloroethane, 1,1-dichloroethane and 1, 1, 1-trichloroethane and their various substituted isotopic species have been observed. From the moments of inertia obtained the complete r_s structures were derived. The comparison of C-C bond lengths in the series of ethane and its chloro-derivatives showed an unusual trend of change. The analysis done by considering small isotopic effects in bond lengths removed the inconsistency and suggests that the molecular parameters derived by using Kraitchman's equations are largely affected by small isotopic displacements when heavy atoms are located far from the center of mass.