Theoretical study on the structure of the trimer consisting of a rare gas atom and two ammonia molecules

Abstract

Recently, the experimental detection and characterization of Van der Waals trimers is a subject of growing interest. In the present study, The potential energy surface for the Ar/(NH3)2 trimer has been explored by using second-order M?ller-Plesset perturbation theory (MP2). Dunning and coworker's correlated consistent aug-cc-pVTZ basis set was employed for the ab initio calculation. Intermolecular potential energy surfaces were calculated at the several geometries for the Ar-(NH3)2 trimer. Two stable isomers were located and the geometries of the two isomers were fully optimized. In the two optimized structures, the NH3-NH3 interaction play an important role in the Ar/(NH3)2 trimer. The structural parameters of (NH3)2 unit in the Ar/(NH3)2 trimer are very similar to the values in the (NH3)2 dimer. This indicate that the structure of the (NH3)2 dimer is nearly unaffected by the weak interaction with the Ar atom. In addition, the local structure of the Ar atom in the global minimum structure for the Ar/(NH3)2 trimer is almost the same as that of the Ar/NH3 dimer.