The reaction of SiH3+ with C2H4 has been studied in a tandem mass spectrometer at relative kinetic energies in the range of 0.47 to 2.4 eV and at C2H4 pressures in the range of 2-80 X Torr. At low relative kinetic energies persistent collision complexes SiC2H7+ are directly observed, in the absence of collisional stabilization, some 2 X s after formation. Collisional stabilization by C2H4 increases the yield of SiC2H7+ so that at 80 X Torr this ion accounts for -80% of the observed products. The other observed products are SiQHS+, SiCH3+, and SiC2H3+. Extrapolation of product yields to infinite pressure indicates that the collision complex accounts for -90% of total reaction with the other 10% of reaction being due to a direct process forming SiCH3+. The experimental data yield absolute values for the lifetime of energy-rich collision complexes, for the unimolecular rate constants for decomposition of the complex to SiC*H5+ and SiCH3+, and for the single-collision stabilization of SiC2H7+* by C2H4. The strong collision assumption breaks down at the higher relative kinetic energies and a value of 0.7-1.1 eV for the maximum energy transferred per collision from SiC2H7+* to C2H4 may be derived. RRKM calculations based on the chemically activated molecule being CH3CH2SiH2+ and in which angular momentum of reactants is conserved give order-of-magnitude agreement with experiment.
The ion-molecule reactions characteristic of SiH.-D 2 mixtures have been elucidated and the reaction cross sections measured as a function of relative kinetic energy. Di reacts with SiH. to yield SiH:, SiHi, SiH+, and Si + by exothermic processes that proceed with a total cross section near the Langevin orbiting value. D: reacts with SiH. to fonn only SiH: with a cross section also near the Langevin value. The absence of SiH 2 D+ suggests direct H-transfer from SiH. rather than the intermediate formation of SiH.D +. All reactions of Si-containing ions in their ground states with D2 are endothermic. Energy thresholds for the deuterium atom pickup reactions of Si+ and SiHi yield thermochemical results in satisfactory agreement with values obtained by other methods. SiH: reacts with D2 to fonn SiH 2 D+ solely. a result indicating that only HD is eliminated from an SiH3Di intermediate and showing the nonequivalence of D and H in the silanium ion.
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