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

摘要

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-center dot) and Me3Si center dot. Me3Si center dot underwent subsequent loss of a hydrogen atom to form Me2Si=CH2 and loss of a methyl radical to form Me2Si:. Isomerizations via 1,2-shift and H-2 eliminations were major secondary decomposition reactions of Me2Si=CH2 and Me2Si:. Among the various isomers, silylene species containing Si-H bonds, such as :Si(H) CH2CH2CH3, :Si(H) CH2CH=CH2, :Si(H)CH2CH3, and :Si(H)CH=CH2, played an important role in H-2 elimination reactions. On the other hand, silene species were insignificant in H-2 eliminations. Unlike the silylene species, H-2 elimination of :Si=CH2 was energetically unfavorable.