STRUCTURAL-CHANGES AS A FUNCTION OF TORSIONAL MOTION STUDIED BY AB-INITIO CALCULATIONS .3. XA-AX (A=O, S AND X=H, F, CL) AND IMPLICATIONS ON COMPARISONS OF STRUCTURAL PARAMETERS FROM AB-INITIO CALCULATIONS ANDELECTRON-DIFFRACTION, AND ON INCLUSION OF ROTATIONAL-CONSTANTS IN AN ELECTRON-DIFFRACTION ANALYSIS

Structural changes as a function of the torsion angle about the centra l A-A bond have been studied for XA-AX type molecules with A = O, S an d X = H, F, Cl by ab initio calculations using standard 6-31G basis s ets. The results from the calculations are compared with the correspon ding experimental values. The implications of the results for a compar ison of the equilibrium structure with the average structure from elec tron diffraction are discussed. The implications on the inclusion of r otational constants from microwave spectroscopy and intensity data fro m electron diffraction in a joint analysis are also considered. These results are the first quantitative estimation of how the average struc ture changes with the potential and temperature and of the consequence s for practical structural work.