According to the results of IR spectroscopic study and quantum--chemical calculations, hydroxo derivatives SiF4_x(OH)x are formed in the course of hydrolysis of silicon tetrafluoride in the presence of small amount of water along with hexafluorodisiloxane.Key words: silicon tetrafluoride, products of hydrolysis; IR spectroscopy, quantumchemical calculations.Silicon tetrafluoride is widely used for producing epitaxial layers of amorphous silicon and as a fluorinating agent in manufacturing SiO 2 fiber light pipes, t For these purposes SiF 4 with extremely low concentrations of oxygen-and/or hydrogen-containing impurities, z especially water and products of the hydrolysis of the main substance, is required. The most informative methods for the determination of impurities in SiF 4 are IR spectroscopy and mass-spectrometry. 3.4 It should be noted that the composition of the impurities in SiF 4 depends strongly on the method of preparation of the latter and the procedure for subsequent purification. Our preliminary study of IR spectra of gaseous SiF 4 synthesized by thermal decomposition of sodium hexafluorosilicate and containing water impurity showed the presence of an intense absorption band in the region near 3764 cm -t and a weaker band at 3860 cm -I. The aim of this work was to study the nature of the band at 3764 cm -I in the IR spectrum of silicon tetrafluoride experimentally and theoretically using ab initio quantum-chemical calculations. ExperimentalSilicon tetrafluoride was obtained by thermal decomposition of soclittm hexafluorosilicate and purified from volatile impurities by cryofiltration followed by rectification on a column with sampling the medium fraction.IR spectra of gaseous SiF 4 in the region 800--4500 cm -I were recorded on Specord MS0 and IFS-120HR instruments with a resolution of 4 cm -] and 0.1 cm -I, respectively. A multipass cell with a length of the optical path (/) of 100 cm and a cell with I = 20 cm with ZnSe windows were used. Spectra of solutions in liquid CCI 4 were obtained in a cell with an optical path length of I0 cm (ZnSe windows) equipped with an inlet system that allowed introducing gaseous SiF 4 and H20. Carbon tetrachloride was purified by rectification until a residual moisture content of 5 9 10 -5 tool.% was achieved.C_.aleulation IK'ocednre. Quantum-chemical calculations of the equilibrium molecular structure and vibrational spectra of possible products of hydrolysis of SiF 4 were carried out by the ab initio SCF method with inclusion of correlation energy according to the density functional theory (DFT) using the B3LYP mixed exchange-correlation functional in the 6-31 IG(d,p) basis set (five-component basis set functions). The geometry optimization and calculations of vibrational frequencies were carried out using the GAUSSIAN 94 program. 5.