Identification of decomposition reactions for HMDSO organosilicon using quantum chemical calculations.

Hexamethyldisiloxane [HMDSO, (CH3)3‐SiOSi‐(CH3)3] is an important precursor for SiO2 formation during flame‐based silica material synthesis. As a result, HMDSO reactions in flame have been widely investigated experimentally, and many results have indicated that HMDSO decomposition reactions occur very early in this process. In this paper, quantum chemical calculations are performed to identify the initial decomposition of HMDSO and its subsequent reactions using the density functional theory at the level of B3LYP/6‐311+G (d, p). Four reaction pathways—(a) SiO bond dissociation of HMDSO, (b) SiC bond dissociation of HMDSO, (c) dissociation and recombination of SiO and SiC bonds, and (d) elimination of a methane molecule from HMDSO—have been examined and identified. From the results, it is found that the barrier of 84.38 kcal/mol and SiO bond dissociation energy of 21.55 kcal/mol are required for the initial decomposition reaction of HMDSO in the first pathway, but the highest free energy barrier (100.69 kcal/mol) is found in the third reaction pathway. By comparing the free energy barriers and reaction rate constants, it is concluded that the most possible initial decomposition reaction of HMDSO is to eliminate the CH3 radical by SiC bond dissociation. [ABSTRACT FROM AUTHOR]