Part I : Kinetic d a t a for t h e s t a t i c system s i l a n e pyrolysis ( f r o m 640-703 K , 60-400 torr) are presented. For conversion from 3-304. first-order kinetics a r e obtained, with silane loss rates equal to half the hydrogen formation rates. At conversions greater than 4 0 4 , rate inhibition attributable to the back reaction of hydrogen with silylene occurs. Overall reaction rates are not surface sensitive. but disilane and trisilane yield maxima under some conditions are. A nonchain mechanism capable of describing quantitatively all stages of the silane pyrolysis is proposed. Post 1.05; initiation is both homogeneous (gas phase) and heterogeneous (on the walls), and reaction intermediates are silylenes and disilenes. Free radicals are not involved a t any stage of the reaction. Rate data a t high conversions and with added hydrogen provide kinetics for the addition of silylene to hydrogen [reaction (-1iI relative to its addition to silane [reaction (2)l: k , / k , = 1 0~0 6 5 x e 3 2 0 " c~i ' H T . With E2 = 1300 cal, this gives a highpressure activation energy for silylene insertion into hydrogen of E -, = 8200 cal.Part 11: An analysis is made of each rate constant of the silane mechanism and the modeling results are compared with experimental results. Agreement is excellent. It is concluded that the dominant sink reaction for silylene intermediates is 1,2-H, elitnination from disilane (followed by SiYHl polymerization and wall deposition). The model is in accord with slow isomerization between disilene and silylsilylene and near exclusive 1,2-H2 elimination from S i L H G .It is also concluded t h a t disilene is about 10 kcal/mol more stable than silylsilylene and that the activation energy for isomerization of silylsilylene to disilene is greater than 26 kcal/;nol.