Ab Initio Intermolecular Potential Energy Surfaces and Cross Second Virial Coefficients for the Dimer N(2)-NO

[Image: see text] Ab initio intermolecular potential energy surfaces (PES) of N(2)-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 X(1)Σ(+) and nitric oxide in the open-shell electronic configuration A(2)Σ(+) 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 N(2)-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 N(2)-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.