MECHANISM OF THE THERMALLY INDUCED GAS-PHASE DECOMPOSITION OF SILANE - A REVISITATION

Modeling of the SiH4 thermal decomposition (640-703 K; 80-320 Torr) ia revisited here since new kinetic data now invalidate our prior modeling. The new data are for silylene insertion reactions, for silylene-disilene isomerizations, and for the H-2 elimination from Si2H6. Three possible sink reactions as balance for silylene productions were examined: (1) reactive intermediate polymerization followed by wall deposition, (2) reactive intermediate decomposition to a nonreactive species followed by wall deposition, and (3) direct reaction of polysilanes (Si3H8 and larger) on the walls. Using rate constants consistent with all present data, the modeling demonstrated that fits to the experimental data could only be achieved with polysilane-wall decompositions as sink reactions. Rate constants for these wall processes were obtained directly from our published Si3H8 decomposition data. In addition, the modeling indicated that best fits to the experimental data were realized with negative activation energies for all silylene Si-H bond insertion reactions in accord with new data on the SiH2 + SiH4 reaction (Walsh et al.).