Thermal decomposition of tetramethylsilane and tetramethylgermane by flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry

• The initial decomposition step of TMS and TMG is loss of a methyl radical to form Si(CH3)3 and Ge(CH3)3, respectively.
• While Si(CH3)3 can lose a second methyl radical to form :Si(CH3)2, it could also undergo sequential H loss, which is reported for the first time in this study.
• H loss and CH4 loss from :Si(CH3)2 are more competitive than the methyl loss.
• Ge(CH3)3 undergoes sequential methyl loss to :Ge(CH3)2, Ge(CH3), and Ge.

Thermal decomposition of tetramethylsilane (TMS) and tetramethylgermane (TMG) was studied on a short time scale of 20–100 μs using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Primary decomposition of TMS and TMG occurred via loss of a methyl radical to form Si(CH3)3 and Ge(CH3)3, respectively. Both the Si(CH3)3 and Ge(CH3)3 radicals underwent secondary loss of a second methyl radical to form :Si(CH3)2 and :Ge(CH3)2, respectively. A previously unobserved secondary decomposition process in TMS involving loss of H atom from Si(CH3)3 followed by elimination of H2 to form SiC3H8, SiC3H6, and SiC3H4 was also identified. Sequential loss of the third and fourth methyl radical with significant formation of Ge and Ge2 was observed in the TMG pyrolysis. Loss of a third methyl radical in the TMS pyrolysis was not significant, while Si and SiC products were possibly produced. Secondary reactions of methyl to form unsaturated CxHy species, particularly in the TMG decomposition, were also observed.

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