Rovibrational dynamics of the quasistructural N2 dimer

Although the collision-induced absorption spectrum of the nitrogen gas is known in considerable detail, little has been learned experimentally about the structural, dynamical, and rovibrational characteristics of the nitrogen dimer itself. This study explores all these properties of this prototypical van der Waals (vdW) dimer and provides definitive quantum chemical results, mostly with attached conservative uncertainty estimates, particularly for the parent isotopologue, ¹⁴N₂⋅¹⁴N₂. The results obtained are based on three analytical representations of the dimer's ground-state potential energy surface (PES), including two full-dimensional models of spectroscopic accuracy, constructed during the present study. The structural and focal-point analyses confirm that the global minimum of (N₂)₂ is planar and has a tilted, Z-shaped form, with an electronic dissociation energy of 109.3(26) cm^-1. After considering zero-point vibrational effects variationally, the first dissociation limit of ¹⁴N₂⋅¹⁴N₂ is estimated to be 72.2(15) cm^-1. The full- and reduced-dimensional variational nuclear-motion computations performed result in almost 6000 bound rovibrational states for ¹⁴N₂⋅¹⁴N₂, including over 100 purely vibrational modes. Effects arising from isotopic substitutions, as well as the shifts and splittings of the two quasi-bound N ≡ N stretch fundamentals, are also examined. An in-depth analysis of the rovibrational eigenstates indicates that N₂⋅N₂ is a quasistructural molecular complex.