Mechanistic Study of Thermal Decomposition of Hexamethyldisilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry and Density Functional Theory

Thermal decomposition of hexamethyldisilane (HMDS) was studied from room temperature to 1310 K using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Decomposition pathways of HMDS and initial reaction intermediates were also investigated using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. Unimolecular decomposition reactions of HMDS involving Si-Si and Si-C bond cleavage, as well as decomposition producing Me₄Si and :SiMe₂ via a three-centered elimination, were determined as the initiation reactions. Me₃SiSi(Me)₂^•, Me₄Si, Me₃Si^•, and :SiMe₂ were major products of the initiation reactions. These initial products were apt to decompose by homolytic reactions. Me₂Si═CH₂, :SiMe₂, and other silene/silylene intermediates preferred decomposing through molecular eliminations. Both homolytic and molecular elimination reactions are important in the pyrolysis of HMDS.