Possible Reaction Routes and Mechanisms

The terms route and mechanism will be used as defined below  

Route a reaction pathway or a series combination of elementary steps which correspond to the overall reaction, no specification being given concerning the rate-controlling nature of the steps. 

Mechanism a route with specifications on the rate-controlling nature of the constituent steps, and their coupling. 

Among various reaction routes proposed so far, it appears reasonable to consider the following two routes other external causes such as ohmic resistivity of the solution, mass-transfer limitations, film formation, etc., will not be considered. 

We shall, however, not dwell on this matter since this would not affect very much the general analysis to be dealt with below, except that the kinetics might be different from those anticipated on the basis of an ordinary Volmer step. Although the formation of Na(a) on the electrode is probably well established, particularly on soft metals, there might still remain a discussion as to Na(a) being actually a reaction intermediate of the HER or simply a by-product. Other reaction routes, involving reaction intermediates such as H2(a), H (a), and solvated electrons,etc. have not gained sufficient experimental support to demonstrate that these species should be 

---