Gas-phase reaction kinetics of 1,3-disilacyclobutane in a hot-wire chemical vapor deposition reactor

The reaction kinetics of the decomposition of 1,3-disilacyclobutane (DSCB) was investigated using a hot-wire chemical vapor deposition reactor. The reaction products were monitored using a vacuum ultraviolet laser single-photon ionization source coupled with a time-of-flight mass spectrometer. Steady-state approximation was used to determine the rate constants for three main decomposition pathways of DSCB: the exocyclic H₂ elimination (k₁), the cycloreversion (k₂), and the ring-opening via 1,2-H shift (k₃). Separate k₂ and k₃ were not obtained, but 2k₂ + k₃ and k₁ were determined. The activation energy (E_a) for the exocyclic H₂ elimination reaction was determined to be 63.5 kJ·mol⁻¹. Compared to the E_a value of 43.6 kJ·mol⁻¹ previously obtained under collision-free conditions at much lower pressures, the value from this work is higher. This is attributed to the filament aging caused by the formation of silicon carbide (SiC) and tungsten sub-carbide (W₂C) on the wire surface. The heterogeneous reactions on the metal surface also led to a much faster decay constant, k_overall, for DSCB than those for each individual decomposition pathway, k₁ and 2k₂ + k₃. - Highlights: • The decomposition kinetics of 1,3-disilacyclobutane in a HWCVD reactor was studied. • The rate constant of exocyclic H₂ elimination from DSCB, k₁, was determined. • 2k₂ + k₃ were determined (k₂ — cycloreversion; k₃ — ring opening via 1,2-H shift). • Filament aging caused an increase in the activation energy for H₂ elimination.