Ab Initio Intermolecular Potential Energy Surfaces and Cross Second Virial Coefficients for the Dimer N₂-NO

Ab initio intermolecular potential energy surfaces (PES) of N₂-NO have been constructed at the level of theory CCSD(T) with the augmented correlation-consistent basis sets aug-cc-pVmZ (with m = 2, 3, 4). The nitrogen in the closed-shell electronic configuration X¹Σ⁺ and nitric oxide in the open-shell electronic configuration A²Σ⁺ were employed to calculate ab initio intermolecular interaction energies. The two new ab initio 5-site intermolecular pair potentials at the theoretical level CCSD(T)/aug-cc-pVmZ (with m = 4, 24) were developed appropriately and are suitable for N₂-NO dimer by using the nonlinear least-squares fitting method combining MIO and Levenberg-Marquardt algorithms. The correlation quality of these two potentials was found to be very good with R ² values in the range of 0.98372 to 0.99775. The cross second virial coefficients B ₁₂(T) of the N₂-NO dimer were calculated in the temperature range of 100 to 470 K using the two ab initio 5-site potentials. The discrepancies between the calculated results and the experimental data can be acceptable.