title: The molecular structure of hexamethyldigermane determined by gas-phase electron diffraction with theoretical calculations for (CH3)3M-M(CH3)3 where M = C, Si, and Ge.
abstract: Gas-phase electron diffraction (GED) data together with results from ab initio molecular orbital calculations (HF and MP2/6-311+G(d,p)) have been used to determine the structure of hexamethyldigermane ((CH(3))(3)Ge-Ge(CH(3))(3)). The equilibrium symmetry is D(3d), but the molecule has a very low-frequency, large-amplitude, torsional mode (phiCGeGeC) that lowers the thermal average symmetry. The effect of this large-amplitude mode on the interatomic distances was described by a dynamic model which consisted of a set of pseudoconformers spaced at even intervals. The amount of each pseudoconformer was obtained from the ab initio calculations (HF/6-311+G(d,p)). The results for the principal distances (r(a)) and angles (angle(h1)) obtained from the combined GED/ab initio (with estimated 1sigma uncertainties) are r(Ge-Ge) = 2.417(2) A, r(Ge-C) = 1.956(1) A, r(C-H) = 1.097(5) A, angleGeGeC = 110.5(2) degrees, and angleGeCH = 108.8(6) degrees. Theoretical calculations were performed for the related molecules ((CH(3))(3)Si-Si(CH(3))(3) and (CH(3))(3)C-C(CH(3))(3)).
authors.affiliation: Oslo University College, Faculty of Engineering, PO Box 4, St. Olavs Plass N-0130 Oslo, Norway.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Aarset
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Page
authors.forename: David A
authors.initials: DA
authors.lastname: Rice