Nitrogen dissociation on Fe: activated, non-activated or both?

Consideration is given to the nature of the dissociation pathway of nitrogen on Fe, an important initial step in ammonia synthesis. In particular, the disagreement over the basic energetics of this process is discussed, that is whether the pathway involves direct or indirect (precursor-mediated) dissociation. It is concluded that under the conditions of industrial ammonia synthesis the dominant process is direct, but that indirect dissociation may pertain under some experimental conditions.