 Thus the polymeric silicon hydrides are formed along with smaller silicon hydride oligomers and hydrogen gas from the spontaneous but slow decomposition, as well as from the accelerated thermolysis, of acyclic and cyclic liquid silanes that are higher in molecular weight than monosilane (SiH4) and disilane (Si2H6).Polysilicon hydrides are intermediates in the high-temperature conversion of mono- and disilane to silicon and hydrogen gas.In the following idealized sequence cyclopentasilane is the polysilicon hydride intermediate