Thermal decomposition mechanism of allyltrichlorosilane and allyltrimethylsilane

Thermal decomposition of allyltrichlorosilane and allyltrimethylsilane at temperatures up to 1340 K were studied using flash pyrolysis coupled with molecular beam sampling and vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). The initial reaction of allyltrichlorosilane was homolysis of the Si–C bond, producing •SiCl3 and •C3H5 radicals. The •SiCl3 radical then underwent sequential Cl losses to form :SiCl2, SiCl and Si. The C3H5 radical also underwent secondary reactions, producing a series of C3Hx species (m/z = 39–42), consistent with previous studies. In the pyrolysis of allyltrimethylsilane, molecular elimination reaction forming Me2Si=CH2 + C3H6 and Si–C bond ruptures producing Me3Si• + •C3H5 and Me2Si˙CH2CH=CH2 + •CH3 were identified as the main initiation decomposition steps. HSiMe3 was also identified as one of the initiation reaction products. The observed secondary reactions of Me2Si=CH2 and Me3Si• were consistent with previous studies. Possible thermal decomposition mechanism of the Me2Si˙CH2CH=CH2 product was also proposed.