Theoretical Studies on Van der Waals Trimers (3):R2/NH3(R=He,Ne,Ar)

Abstract

The study of intermolecular interactions is a useful step toward gaining a basic understanding of the dynamic behaviour of molecules in various environments. Especially, interactions of the ammonia (NH3) molecule with other molecules provide valuable information on protein-protein interactions or protein-solvent interactions in biological systems. From this point of view, high-level ab initio calculations [MP2] using correlation consistent basis sets of Dunning [aug-cc-pVTZ] were carried out to study the structures and stability of He2/NH3, Ne2/NH3 and Ar2/NH3 Van der Waals trimers and to clarify the nature of three-body interactions. For the most stable structure of He2/NH3, each He atom is located midway between two of the NH3 hydrogen atoms. On the other hand, the global minima on the potential energy surface of Ne2/NH3 and Ar2/NH3 occur at geometries in which a N-H axis of NH3 directed toward one of the rare gas atoms and the other rare gas atom midway between two of the NH3 hydrogen atoms. He-He interaction in He2/NH3 is considerably weaker than in He2 dimer. However, for the Ne2/NH3 and Ar2/NH3, the interactions between two rare gas atoms are almost as strong as in rare gas dimers.