The energies and thermodynamic parameters of the elementary reactions involved in the gas-phase hydrolysis of silicon tetrachloride were studied using ab initio quantum chemical methods (up to MP4//MP2/6-311G-(2d,2p)), density functional (B3LYP/6-311++G(2d,2p)), and G2(MP2) theories. The proposed mechanism of hydrolysis consists of the formation of SiCl 4-x , chainlike and cyclic siloxane polymers [-SiCl 2 sO-] n , dichlorosilanone Cl 2 SidO, and silicic acid (HO) 2 SidO. Thermodynamic parameters were estimated, and the transition states were located for all of the elementary reactions. It was demonstrated that the experimentally observed kinetic features for the hightemperature hydrolysis are well described by a regular bimolecular reaction occurring through a four-membered cyclic transition state. In contrast, the low-temperature hydrolysis reaction cannot be described by the traditionally accepted bimolecular pathway for SisCl bond hydrolysis because of high activation barrier (E a ) 107.0 kJ/mol, ∆G q ) 142.5 kJ/mol) nor by reactions occurring through three-or four-molecular transition states proposed earlier for reactions occurring in aqueous solution. The transition states of SiCl 4 with oneand two-coordinated water molecules were located; these significantly decrease the free energy of activation ∆G q (to 121.3 and 111.5 kJ/mol, correspondingly). However, this decrease in ∆G q is not sufficient to account for the high value of the hydrolysis rate observed experimentally under low-temperature conditions.

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-The impurity compositions of silicon tetrafluoride and silane prepared from it have been determined by high-resolution Fourier-transform IR spectroscopy. In the spectra of SiF 4 samples differing in purity, we have identified rovibrational bands arising from Si 2 F 6 O, SiF 3 OH, HF, SiF 3 H, SiF 2 H 2 , SiH 3 F, CH 4 , CO 2 , and CO impurities. Their detection limits lie in the range 9 × 10 -5 (CO 2 ) to 3 × 10 -3 mol % (Si 2 F 6 O). In the spectra of SiH 4 samples of different purity, we have detected CH 4 , CO 2 , SiF 3 H, SiF 2 H 2 , and SiF 4 impurities. Their detection limits lie in the range 8 × 10 -5 (CO 2 ) to 1 × 10 -3 mol % (SiF 4 ).

-The spectral characteristics of the SiF 4 molecule in the range 3100-700 cm -1 , including the absorption range of the band ν 3 , are studied in the gas phase at P = 0.4-7 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 2 ν 3 , ν 3 + ν 1 , ν 3 + ν 4 , and 3 ν 4 are measured in the solution in Kr. In the gas phase of the one-component system at an elevated pressure of SiF 4 , the integrated absorption coefficient of the absorption band ν 3 of the 28 SiF 4 molecule was measured to be A ( ν 3 ) = 700 ± 30 km/mol. Within the limits of experimental error, this absorption coefficient is consistent with estimates obtained from independent measurements and virtually coincides with the coefficient A ( ν 3 ) = 691 km/mol calculated in this study by the quantum-chemical method MP2(full) with the basis set cc -p VQZ .

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