Figure 2.

(A) Dependence of the Mn²⁺ EPR signal intensity on bicarbonate concentration in aqueous solution at room temperature (Mn²⁺ concentration 0.5 mM, pH 8.3). Fit to an equilibrium model described in Eqn. 8 is shown with solid line. Inset shows typical Mn²⁺ EPR signal in aqueous solution centered at g 2.0. (B) Dependence of the Mn²⁺ EPR signal intensity (normalized to total amount of Mn²⁺ in the sample) as a function of Mn²⁺ concentration at fixed 50 mM NaHCO₃ in aqueous solution at room temperature. The straight line shows the invariance on Mn²⁺ concentration, clearly eliminating the presence of any Mn²⁺ clusters in speciation.