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 Me2Si[double bond, length as m-dash]CH2 and loss of a methyl radical to form Me2Si:. Isomerizations via 1,2-shift and H2 eliminations were major secondary decomposition reactions of Me2Si[double bond, length as m-dash]CH2 and Me2Si:. Among the various isomers, silylene species containing Si-H bonds, such as :Si(H)CH2CH2CH3, :Si(H)CH2CH[double bond, length as m-dash]CH2, :Si(H)CH2CH3, and :Si(H)CH[double bond, length as m-dash]CH2, 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 :Si[double bond, length as m-dash]CH2 was energetically unfavorable.
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. Me2SiCH2, :SiMe2, and other silene/silylene intermediates
preferred decomposing through molecular eliminations. Both homolytic
and molecular elimination reactions are important in the pyrolysis
of HMDS.
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