Kinetic and Thermodynamic Considerations in On-Surface Synthesis

Abstract

In this chapter it will be explained how kinetic and thermodynamic aspects of on-surface reactions may be accounted for by electronic structure theory together with transition state theory. The focus of the chapter is to discuss what free energy contributions, particularly in terms of entropy, we need to account for to properly describe chemical reactions on surfaces. For example, dehydrogenation reactions are often endothermic and their occurrence on surfaces can be explained by the entropy gain of associatively desorbing hydrogen, which make them thermodynamically favorable. In another example, experimentally observed intermediate structures of a bimolecular enediyne coupling were concluded to be stabilized by differences in surface dissipation of excess energy and translational entropy, requiring a quite complex free energy description to understand the reaction. Calculating reaction pathways is becoming a frequent practice within on-surface synthesis, but are often considered at 0 K to reduce computational efforts. The recent advances in describing in particular entropic contributions of on-surface reactions provide important guidelines for how calculations can be refined, and for what kind of scenarios we may expect the necessity for more sophisticated descriptions of kinetics and thermodynamics of reactions.