Structure, spectra, and intramolecular motions of 1,4-bis(trimethylsilyl)-1,3-butadiyne: an electron diffraction study using the results of spectral analysis based on scaled quantum-chemical force field for calculating vibrational effects

The molecular structure of 1,4-bis(trimethylsilyl)-1,3-butadiyne has been s tudied by the gas electron diffraction method and by ab initio calculations at the RHF and MP2 levels. A scaled quantum-chemical force field was used to interpret the vibrational spectra, The root-mean-square vibrational ampl itudes and harmonic shrinkage corrections were calculated taking into accou nt non-linear relations between Cartesian and internal vibrational co-ordin ates at the level of first-order perturbation theory (hl) and with the use of the traditional scheme (h0), The total energies of the D-3d and D-3h con formers differ by about 1 cal mol(-1) (0.4 cm(-1)) which implies virtually free internal rotation, It has been shown that the flexibility of the linea r fragment in (CH3)(3)Si-C dropC-C dropC-Si(CH3)(3) has increased considera bly compared to that in (CH3)(3)Si-C dropC-Si(CH3)(3). (C) 2001 Elsevier Sc ience B.V, All rights reserved.