SiH4 decomposition mechanism

The initial pyrolysis reaction of SiH4 has been explored extensively (98), and the growing consensus is that the thermal decomposition of SiH4 involves the elimination of H2 to form silylene, as shown in equation 1 (98, 101). Possibly, thermal pyrolysis is controlled by heterogeneous reactions on hot surfaces (102, 103), but this hypothesis is controversial, and considerable experimental evidence for a gas decomposition mechanism exists (98). However, at low pressures and high temperatures, heterogeneous decomposition will likely be important in the overall mechanism (104). 

Si-H bonds may give rise to excited adducts which subsequently decompose to give SiH. The same insertion-decomposition cycle may be repeated to yield SiHj, which eventually inserts into the Si-H bond of SiH4 to give SiHjSiHj as the final product. At present, there is no evidence favoring one of these two mechanisms over the other. If the direct H-abstraction process does prevail, there is also no guarantee that the H abstraction is a consecutive instead of a simultaneous process. 

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