The electron transfer kinetics of monolayers of CpFeCpCO(2)(CH2)(12)SH and CH3(CH2)(11)SH co-chemisorbed on gold electrodes have been measured in 2:1 (v:v) chloroethane/butyronitrile solvent at temperatures ranging from 125K to 175K with potential steps and cyclic voltammetry. Rate constants, k degrees, measured using cyclic voltammetry range from 3 x 10(-4) to 10(-1) s(-1) over these temperatures; an:activation plot of log[k degrees/k(b) T-1/2] vs. 1/T gave lambda = 0.89 eV for the reorganization energy for the Cp(2)Fe(+/0) reaction and a pre-factor of 6.5 x 10(6) eV(-1+s-1). 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 CpFeCpCO(2)(CH2)(12)SH monolayers are kinetically inhomogeneous (disperse) as shown by non-linear In[i] 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(app,eta,,) against overpotential (eta), producing depressed values for lambda.