Mechanism of the thermal decomposition of tetramethylsilane: a flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry and density functional theory study

Abstract

The thermal decomposition of tetramethylsilane (TMS) was studied over the temperature range of 298–1450 K by combining flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and density functional theory (DFT). The initial step in TMS pyrolysis produced a methyl radical (Me˙) and Me₃Si˙. Me₃Si˙ underwent subsequent loss of a hydrogen atom to form Me₂SiCH₂ and loss of a methyl radical to form Me₂Si:. Isomerizations via 1,2-shift and H₂ eliminations were major secondary decomposition reactions of Me₂SiCH₂ and Me₂Si:. Among the various isomers, silylene species containing Si–H bonds, such as :Si(H)CH₂CH₂CH₃, :Si(H)CH₂CHCH₂, :Si(H)CH₂CH₃, and :Si(H)CHCH₂, played an important role in H₂ elimination reactions. On the other hand, silene species were insignificant in H₂ eliminations. Unlike the silylene species, H₂ elimination of :SiCH₂ was energetically unfavorable.