The structure and spectra of 1-silylpropyne: scaled quantum-chemical forcefields and vibrational effects

The geometric parameters and the force fields of two 1-silylpropyne conform ers (eclipsed and staggered, both of C-3v symmetry) were calculated by the restricted Hartree-Fock method and taking into account electron correlation in the approximation of Moller-Plesset second-order perturbation theory (6 -311G** basis set). The total energies of the two conformers differ by less than 20 cal mol(-1), which is evidence of virtually free internal rotation . The IR spectra of H3SiC equivalent to CCH3 and D3SiC equivalent to CCH3 w ere interpreted by scaling quantum-chemical force fields. The scale factors were found to be transferable in the series of Si and Sn acetylenides. The mean vibrational amplitudes and the harmonic corrections to internuclear d istances were calculated taking into account nonlinear kinematic effects. C orrections for centrifugal distortions and anharmonic effects were calculat ed at the level of first-order perturbation theory. The introduction of the se corrections into the experimental r(ij,a) parameters allowed us to deter mine the parameters of the r(h1) structure and estimate:equilibrium internu clear distances. (C) 2001 Elsevier Science B.V. All rights reserved.