Hougen’s theory

Hougen s construct thus provides considerable simplification of the theory of the general linear molecule and has been used, often unknowingly, by countless authors. We use it with gratitude throughout this book. 

For a reaction of such complexity as methanation (or FTS) an exact kinetic theory is actually out of the question. One has to introduce one or more approximations. The usual assumption made is that one reaction step is rate determining (r.d.s.) and other steps are in equilibrium or steady state. Adsorption equilibria are described by Langmuir formulas (Langmuir-Hinshelwood, Hougen-Watson... 

The analysis of the relativistic Renner coupling has been extended to 11 states, including the two-electron part of the Breit-Pauli operator, thus generalizing previous result of Hougen [45,46]. Other extensions of the theory are S — 11 coupling in the doublet manifold [47] and SO coupling in a half-filled n shell, as found, for example, in carbenes [48]. 

---