Mechanism and Product Branching Ratios of the SiH₃ + SiH₃ Reaction

The mechanism of the SiH 3 + SiH 3 reaction was studied by means of time resolved mass spectrometry. SiH 3 radical was generated by the ArF laser photolysis of C 2 Cl 4 in SiH 4 /He mixtures, and the products were detected by a low-energy electron impact ionization mass spectrometer. The rate constant derived from the decay rate of SiH 3 agreed well with that obtained from the rise rate of Si 2 H 6 . The overall rate constant of the reaction at 297 ± 2 K was determined to be (9.5 ± 3.5) × 10 -11 cm 3 molecule -1 s -1 . H 2 could also be detected as a product of the SiH 3 + SiH 3 reaction, and the yield of H 2 was measured to be 11 ± 4%. The other major product of the SiH 3 + SiH 3 reaction was SiH 2, which rapidly reacts with SiH 4 to form Si 2 H 6 . It was confirmed by the addition of a large amount of H 2 as a SiH 2 -trapping reagent that Si 2 H 6 detected at p = 5 Torr was exclusively produced via the SiH 2 + SiH 4 reaction. On the basis of these observations, the branching ratios for the decomposition of vibrationally excited Si 2 H 6 produced by the SiH 3 + SiH 3 reaction were estimated. These results were compared with conventional RRKM calculations.