Structure, spectra and internal rotation of bis(trimethylsilyl) acetylene:: spectral analysis by scaling quantum-chemical force fields and two methods for calculating vibrational effects

The geometric parameters of two bis(trimethylsilyl)acetylene conformers (D-3d and D-3h) were calculated by the restricted Hartree-Fock method and taking into account electron correlation as Moller-Plesset second-order perturbations with the use of the 6-31G*, 6-31G'* and 6-311G** basis sets. The D3d and D3h forms correspond to the minimum and the maximum, respectively, of the potential energy curve for internal rotation of the trimethylsilyl group. The total energies of the conformers differ by less than 10 cal mol(-1), which implies virtually free rotation. Scaled quantum-chemical force fields were used to interpret the vibrational spectra of the light and fully deuterated isotopomers. The effect of taking into account nonlinear relations between the Cartesian and internal coordinates on root-mean-square amplitude and shrinkage effect values are analyzed. (C) 2000 Elsevier Science B.V. All rights reserved.