We have studied the reactions of the gas-phase first transition series metal ions Sc+ through Zn+ with CH4, C2H6, and C3Hg in the multicollision environment of He buffer gas at 0.75 Torr. Laser vaporization of pure metal targets creates reactant metal ions M+ in a fast flow reactor. For each primary M+ + alkane reaction step we obtain quantitative effective bimolecular rate constants and product branching fractions. The multicollision rate constants provide a strikingly different view of M+-alkane interactions than previous single-collision studies. At 0.75 Torr, all 10 M+ species react with all 3 alkanes with the single exception of the Mn+ + CH4 pair. Stabilization of long-lived adduct ions of stoichiometry M(alkane)+ by third-body collisions with He is the dominant process in most reactions, although H2 and CH4 elimination channels do occur for the same M+-alkane pairs that undergo single-collision elimination reactions. The rate constants vary widely and nonmonotonically across the transition series for a given alkane in a pattern that is remarkably similar for CH4, C2H6, and C3Hg. This similarity argues against direct insertion of M+ into C-C bonds as the initial step of the M+-alkane interaction, even for those reactant pairs that yield CH4 elimination products. From a simple collisional quenching model we obtain estimates of the time scale for the decay of long-lived hot adduct ions both backwards to reactants and forwards to elimination products. The experimental results suggest that the M+-alkane attractive forces that control the lifetime of the hot adduct ion involve either a donor-acceptor interaction or C-H bond insertion of the metal ion, i.e., strong chemical interactions rather than simple electrostatic forces. For the relatively inert ions Mn+ and Zn+, the dissociation energies Z)°(M+-alkane) exceed 10 kcal/mol. A qualitative model including the interplay of M+ size effects on long-range repulsive forces, of potential surface intersections, and of orbital symmetry and electron spin conservation effects can explain much of the existing M+-alkane reaction data in both multicollision and single-collision environments.

A series of experiments which lead to observations about the reactivity of nickel. [Debut]