In situ diagnostics of the decomposition of silacyclobutane on a hot filament by vacuum ultraviolet laser ionization mass spectrometry

The gas-phase reaction products of silacyclobutane (SCB) and 1, 1-dideuterio-silacyclobutane (SCB-d(2)) from a hot-wire chemical vapor deposition (HWCVD) chamber were diagnosed in situ using vacuum ultraviolet (VUV) laser single-photon ionization (SPI) coupled with time-of-flight (TOF) mass spectrometry. The SCB molecule was found to decompose at a filament temperature as low as 900 degrees C. Both Si- (silylene, methylsilylene, and silene) and C-containing (ethene and propene) species were produced from the SCB decomposition on the filament. Ethene and propene were detected by the mass spectrometer. It is demonstrated that the formation of ethene is favored over that of propene. The experimental study of hot-wire decomposition of SCB-d(2) shows that propene is most likely produced by a process that is initiated by a 1,2-H(D) migration to form n-propylsilylene, followed by an equilibration with silacyclopropane, which then decomposes to propene. The detection of ethene in our experiment indicates that a competitive route of fragmentation exists for SCB decomposition on the filament. It has been shown that this competitive route occurs without H/D scrambling. The highly reactive silylene, silene, and methylsilylene species produced from SCB decomposition underwent either insertion reactions into the Si-H bonds of the parent molecule or pi-type addition reaction across the double and triple CC bonds. The dimerization product of silene, 1,3-disilacyclobutane, at m/z = 88 was also observed.