SEQUENTIAL REACTIONS OF SID2+ WITH SID4

The thermal (300 K) reaction of SiD2+ with SiD4 proceeds at greater than the Langevin collision rate (21 +/- 3 x 10(-10) cm3/molecule s). The reaction products SiD3+, Si2D2+, and Si2D4+ are produced in a 54:7:39 ratio. Both silicon isotope exchange and adduct (Si2D6+) formation are < 1% of the collision rate at silane pressures of 1-4 x 10(-7) Torr. The branching ratio for SiD3+ formation increases with increasing internal energy of SiD2+. Sequential reactions of SiD3+ and Si2D2+ with SiD4 have been previously found to produce terminal species containing five silicon atoms. Si2D4+ reacts with SiD4 only by silicon isotope exchange at 2.0 +/- 0.7% of the collision rate (0.20 +/- 0.07 x 10(-10) cm3/molecule s) with no evidence of other reactions (< 0.5% of the collision rate). Reaction of SiD2+ with SiD4 does not lead to uncontrained clustering and particle formation in silane plasmas. High level ab initio calculations on this system are reported by Raghavachari in his companion paper. Energies of the critical intermediates and transition states along the reaction surface are compared quantitatively to the experimental results via phase space calculations. The energies agree to within 6 kcal/mol.