Single-atom gas formation enthalpy

Evaluation of Single-Atom Gas Formation Enthalpy (AHgO).63... 

In the experimental evaluation method of single-atom gas formation enthalpy from solids, a known thermodynamic identity can be used ... 

The heats of formation of chemical elements in standard state are taken as zero. The list of such elements is known, for example, [13] and mainly incorporates elements in solid state. Thus the single-atom gas formation enthalpy in these cases equals the sublimation enthalpy and is determined by physical and chemical criteria of the process. The sublimation comes to diffusion movements of heated particles into the surface layer with further effusion (outflow). The diffusion activation energies in external and internal regions are quite different... 

---