Calculation of Root-Mean-Square Amplitudes,Perpendicular Amplitues and Centrifugal Diatortions for 1, 1, 2, 2-tetrachloroethane

Two essntial types of experimental methods. namely gas phase electron diffraction （GED） and rotational specroscopy are used for determining gas molecalar strureture. It should be noted that the definition of interatomic distance obtained by the above methods is usually different. In GED metods the scattered electron intensity by molecule is calculated from the r_a type distance. Because of the effect of vibration,an average nuclear distance at thermal eguilibrium r_a is often adopted. The convesion from r_a to r_a can be achieved by calculation using the mean-root-square amplitUdes （l）, the perpendicular amplitude corrections （K） and the centrifugal distortions （δ_r）. In this paper 1, 1, 2, 2-tetrachloroethane （TCE） is used as an example to describe the calculation of l,K and δ_r, the results of which are found in a good agreement with our observation. So this paper has much more significance on refinedly defining molecular structure and better applying spectrum informations.