REACTIONS OF FE- ELECTRONIC-STATE EFFECTS, COMPARISON TO REACTIONS WITH METHANE, AND M(+)-SIHX (X=0-3) BOND-ENERGIES(, CO+, AND NI+ WITH SILANE )

Guided ion beam techniques are used to measure cross sections as a fun ction of kinetic energy for the reaction of SiH4 with M(+) = Fe+, Co+, and Ni+. Ionic products include MSiH(x)(+) (x = 0-3), as well as MH() and SiH3+. No structural information concerning the MSiH(x)(+) speci es is obtained in the present results. The major low-energy process in all three systems is formation of MSiH(2)(+) + H-2, while at higher e nergies, formation of MH(+) + SiH3 (M = Fe and Co) or SiH3+ + MH (M = Ni) dominates the reactivity. Variation of source conditions allows th e effect of electronic excitation on the reactivity of Fe+ to be studi ed in detail. The a(4)F first excited state of Fe+ is more reactive by approximately an order of magnitude than the a(6)D ground state and h as a different product distribution. The reactivity of Fe+ (a(4)F) is found to closely resemble that of ground state Co+ (a(3)F), which is a pproximately half as reactive as ground state Ni+ (a(2)D). The reactiv ity of these systems may be understood in terms of simple molecular or bital and spin conservation arguments. The thresholds for Fe+, Co+, an d Ni+ reactions are evaluated to yield 0 K bond dissociation energies (BDEs) for M(+)-Si, M(+)-SiH, M(+)-SiH2, and M(+)-SiH3 of 2.87 +/- 0.0 9, 2.63 +/- 0.13, 1.88 +/- 0.09, and 1.90 +/- 0.09 eV, respectively, f or M = Fe; 3.25 +/- 0.07, 3.03 +/- 0.16, 2.25 +/- 0.08, and 1.96 +/- 0 .13 eV, respectively, for M = Co; and 3.34 +/- 0.07, 3.38 +/- 0.15, gr eater than or equal to 2.39 +/- 0.07, and 1.91 +/- 0.12 eV, respective ly, for M = Ni. Evaluation of thresholds for SiH3+ + MH formation (M = Fe, Co, and Ni) is combined with previous studies in our laboratories to yield 0 K BDEs for Fe-H of 1.52 +/- 0.05 eV, for Co-H of 1.95 +/- 0.05 eV, and for Ni-H of 2.56 +/- O.11 eV.