The corrosion films on iron in aqueous carbonate/bicarbonate solutions were studied as a function of concentration, pH, and temperature by using the technique of surface-enhanced Raman spectroscopy with electrodeposited silver. Both Fe(OH)(2) and Fe3O4 were detected in the surface oxide film at prepassivation potentials. Iron carbonate (siderite) was observed in the corrosion film in a limited pH, temperature, and applied potential range. At lower carbonate/bicarbonate concentration (e.g., 0.01 M), passivation was lost, and continuous anodic dissolution of the iron occurred. The cathodic reduction of the corrosion film was enhanced at 75 degrees C.