DECOMPOSITION OF PERCHLORODISILOXANE

The perchlorodisiloxane Si2OCl6 is studied ab initio with a series of basis sets and inclusion of electron correlation at the MP2 level. The molecular structure was investigated with special focus on the sensit ive SiOSi angle and compared with experimental values as well as with the theoretically extensively surveyed Si2OH6. On the basis of 6-311 G(2d) geometries and MP2 energies the cleavage of SiCl bonds in depen dence of the substitution of chlorine by oxygen on an Si center of mod el siloxanes was investigated. We deduce that reactions will start at SiCl3 and SiCl2 groups of chlorosiloxanes, because these groups lose C l atoms most easily. The investigation of the structure and fragmentat ion of Si2OCl6 revealed that a split into SiOCl2 and SiCl4 is competit ive to chlorine abstraction as an initial decomposition reaction. Our calculated reaction energies imply that particle growth in the chemica l vapor deposition leading towards SiO2 will proceed uniformly with li ttle variation in the oxygen content in agreement with experimental fi ndings. (C) 1998 Elsevier Science B.V. All rights reserved.