Second Virial Coefficients for N ₂ ···H ₂ and NH···NH

Thermodynamic properties of real gases can be accurately described using realistic intermolecular potential energy surfaces. In this work, a first-order correction to the ideal gas equation of state is introduced through the computation of the classical second virial coefficient, <i>B</i>(<i>T</i>), derived from the configurational partition function, which explicitly depends on the intermolecular interaction potential. As a case study, the double many-body expansion (DMBE) potential energy surface for the ground electronic state of the N₂H₂ system was employed to derive pairwise interaction potentials for H₂···N₂ and NH···NH. These potentials were used to numerically evaluate the canonical partition function. Second virial coefficients, compressibility factors, and constant-volume heat capacities were computed in the temperature range 30-2000 K. The calculated <i>B</i>(<i>T</i>) values for H₂···N₂ are in good agreement with previous literature data, while the results for NH···NH lie within expected trends observed for similar systems.