The Si-Sn chemical bond: an integrated thermochemical and quantum mechanical study of the SiSn diatomic molecule and small Si-Sn clusters.

The silicon-tin chemical bond has been investigated by a study of the SiSn diatomic molecule and a number of new polyatomic Si(x)Sn(y) molecules. These species, formed in the vapor produced from silicon-tin mixtures at high temperature, were experimentally studied by using a Knudsen effusion mass spectrometric technique. The heteronuclear diatomic SiSn, together with the triatomic Si(2)Sn and SiSn(2) and tetratomic Si(3)Sn, Si(2)Sn(2), and SiSn(3) species, were identified in the vapor and studied in the overall temperature range 1474-1944 K. The atomization energy of all the above molecules was determined for the first time (values in kJ mol(-1)): 233.0+/-7.8 (SiSn), 625.6+/-11.6 (Si(2)Sn), 550.2+/-10.7 (SiSn(2)), 1046.1+/-19.9 (Si(3)Sn), 955.2+/-26.8 (Si(2)Sn(2)), and 860.2+/-19.0 (SiSn(3)). In addition, a computational study of the ground and low-lying excited electronic states of the newly identified molecules has been made. These electronic-structure calculations were performed at the DFT-B3LYP/cc-pVTZ and CCSD(T)/cc-pVTZ levels, and allowed the estimation of reliable molecular parameters and hence the thermal functions of the species under study. Computed atomization energies were also derived by taking into account spin-orbit corrections and extrapolation to the complete basis-set limit. A comparison between experimental and theoretical results is presented. Revised values of (716.5+/-16) kJ mol(-1) (Si(3)) and (440+/-20) kJ mol(-1) (Sn(3)) are also proposed for the atomization energies of the Si(3) and Sn(3) molecules.