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

The geometric parameters and the force fields of two 1-silylpropyne conformers (eclipsed and staggered, both of C3v symmetry) were calculated by the restricted Hartree–Fock method and taking into account electron correlation in the approximation of M?ller–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 H3SiCCCH3 and D3SiCCCH3 were 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 distances were calculated taking into account nonlinear kinematic effects. Corrections for centrifugal distortions and anharmonic effects were calculated at the level of first-order perturbation theory. The introduction of these corrections into the experimental rij,a parameters allowed us to determine the parameters of the rh1 structure and estimate equilibrium internuclear distances.