title: Reactions of Hexa-aquo Transition Metal Ions with the Hydrated Electron up to 300 °C.
abstract: Reactions of the hydrated electron with divalent aqueous transition-metal ions, Cd(2+), Zn(2+), Ni(2+), Cu(2+), Co(2+), Fe(2+), and Mn(2+), were studied using a pulse radiolysis technique. The kinetics study was carried out at a constant pressure of 120 bar with temperatures up to 300 °C. The rate constants at room temperature agree with those reported in the literature. The reaction of Cd(2+) is approximately diffusion-limited, but none of the first-row transition-metal ion reactions are diffusion-controlled at any temperature studied. The activation energies obtained from the Arrhenius plots are in the range 14.5-40.6 kJ/mol. Pre-exponential factors are quite large, between 1 × 10(13) and 7 × 10(15) M(-1) s(-1). There appears to be a large degree of entropy-enthalpy compensation in the activation of Zn(2+), Ni(2+), Co(2+), and Cu(2+), as the larger pre-exponential factors strongly correlate with higher activation energy. Saturation of the ionic strength effect suggests that these reactions could be long-range nonadiabatic electron "jumps", but Marcus theory is incompatible with direct formation of ground state (M(+))aq ions. A self-consistent explanation is that electron transfer occurs to excited states derived from the metal 4s orbitals. The ionic strength effect in the Mn(2+) and Fe(2+) reactions suggests that these proceed by short-range adiabatic electron attachment involving breakdown of the water coordination shell.
authors.affiliation: Notre Dame Radiation Laboratory & Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556 United States.
authors.forename: Kotchaphan
authors.initials: K
authors.lastname: Kanjana
authors.affiliation: Notre Dame Radiation Laboratory & Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556 United States.
authors.forename: Bruce
authors.initials: B
authors.lastname: Courtin
authors.affiliation: Notre Dame Radiation Laboratory & Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556 United States.
authors.forename: Ashley
authors.initials: A
authors.lastname: MacConnell
authors.affiliation: Notre Dame Radiation Laboratory & Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556 United States.
authors.forename: David M
authors.initials: DM
authors.lastname: Bartels