Diffusively bound magnesium ions

The species R—X and Mg " are radical ions." The subscript s is meant to indicate that the species so marked are bound to the surface of the magnesium. Its is known that this is a surface reaction." It has been suggested that some of the R-radicals diffuse from the magnesium surface into the solution and then return to the surface to react with the XMg. There is evidence both for" and against" this suggestion. Another proposal is that the fourth step is not the one shown here, but... 

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