Electron diffraction analysis of XY 2 and XY 3 molecules with large amplitude motion : Part II. Survey of experimental studies

Abstract

A survey is given on the application of the interpretational scheme formulated in Paper I of this series to the analysis of gas phase electron diffraction data on MnF 2, FeF 2, CoF 2, NiF 2, CrF 2 and ZnF 2 conjointly with spectroscopic or estimated vibrational frequencies available from the literature. The results of an analysis by a conventional scheme of interpretation in terms of thermally averaged internuclear distances and amplitudes of vibration are also described. The bending potentials of all the above molecules were found to be shallow. Dynamical behavior of these systems conforms to the pattern of a fairly felxible quasi-linear molecule exhibiting large amplitude bending motion. The bending frequencies estimated independently from electron diffraction data are presented and the results of a numerical calculation of bending vibration spectra are reported. The equilibrium MeF distances, bond angle mean-square displacements and best fit stretching frequencies have also been given. A similar analysis of diffraction data on CrF 3 and LaCl 3 is described. CrF 3 is shown to be a planar molecule exerting large amplitude out-of-plane motion. By contrast, LaCl 3 appears to be pyramidal enough with four lowest doubly degenerated levels located inside both wells of the inversion potential. The fifth level exhibits apparent inversion splitting associated with tunneling of the metal atom, whereas at higher levels of excitation nearly free inversion motion is likely to occur. The equilibrium CrF and LaCl distances and best fit skeletal frequencies optimized against electron diffraction data and spectroscopic or estimated vibrational frequencies available from the literature are presented. The inversion frequencies estimated independently from electron diffraction are also given. By taking CrF 2 as an example, confirmative evidence is given for the potentially fruitful application in diffraction analysis of nonrigid molecules of multidimensional classical and semiclassical distribution functions in cases where appropriate conditions for their adequate use are satisfied.