Electron Transfer Kinetics of Self-Assembled Ferrocene C(12) Alkanethiol Monolayers on Gold Electrodes From 125K to 175K,

The electron transfer kinetics of monolayers of CpFeCpCO2CH212SH and CH3Ch211SH co-chemisorbed on gold electrodes have been measured in 21 vv chloroethanebutyronitrile solvent at temperatures ranging from 125K to 175K with potential steps and cyclic voltammetry. Rate constants, k deg, measured using cyclic voltammetry range from 3x10exp-4 to 10exp-1s over these temperatures an activation plot of logK DEGKSUB BETAT12 vs. 1T gave Lambda 0.89 eV for the reorganization energy for the Cp2Fe0 reaction and a pre-factor of 6.5X10exp 6 eV-1s. The rate constants were obtained by comparison of experimental delta E PEAK values with those of cyclic voltammograms digitally simulated with Marcus-DOS theory. A value of Lambda 0.76 eV is predicted from dielectric continuum theory. The CpFeCpCO2CH212SH monolayers are kinetically inhomogeneous disperse as shown by nonlinear 1nI vs. time plots in potential step experiments. The kinetic dispersity has adverse effects on determinations of Lambda values from cyclic voltammetric waveshapes and from plots of potential step-derived rate constants, k sub app,tau, against overpotential eta, producing depressed values for Lambda. jg