Intermolecular potential energy surface of the N2-CO dimer: ab initio investigation and analytical representation.

In this work, for the first time, an analytical four-dimensional representation for the intermolecular potential of the N(2)-CO dimer is constructed from ab initio calculations. The most stable structure of dimer is found to be a distorted T-shape conformation with CO forming the top and N(2) the leg of T. Important structures of the dimer are characterized, and surprisingly, it is found that in contrast with general assumptions, the potential energy surface of the N(2)-CO dimer has a single symmetry unique minimum. The energy profile of a minimum energy path that connects two T-shaped saddle points to the minimum structure is derived. Important structures are characterized along this path to represent the concerted internal rotation of monomers within the complex. The second virial coefficient is calculated from the fitted PES, and reasonable agreement is found with recent experimental results.