Cross Second Virial Coefficients of the N2–H2, O2–H2, and CO2–H2 Systems from First Principles

Abstract The cross second virial coefficients B₁₂ B 12 for interactions of molecular nitrogen (N 2) with molecular hydrogen (H 2), of molecular oxygen (O 2) with H 2, and of carbon dioxide (CO 2) with H 2 were obtained at temperatures ranging from 36 K to 2000 K for the former two systems and from 100 K to 2000 K for the latter system from new rigid-rotor intermolecular potential energy surfaces (PESs) for the three molecule pairs. Each PES is based on interaction energies calculated for a large number of pair configurations employing high-level quantum-chemical ab initio methods up to coupled cluster with single, double, triple, and perturbative quadruple excitations CCSDT (Q). Core-core and core-valance correlation and relativistic effects were accounted for as well. B₁₂ B 12 values were extracted from the PESs classically and semiclassically using the Mayer-sampling Monte Carlo approach. The deficiencies of the semiclassical calculations at the lowest temperatures were partly remedied by a more rigorous treatment of translational quantum effects using the phase-shift method. The results for the N 2 –H 2 and CO 2 –H 2 systems are in excellent agreement with the most accurate experimental data. For the O 2 –H 2 system, there are no experimental B₁₂ B 12 data because this mixture is highly explosive. There are, however, previous first-principles results for B₁₂ B 12 of this system by Van Tat and Deiters Chem. Phys. 457, 171–179 (2015), which were obtained at a much lower level of sophistication for both the PES and the method to extract B₁₂ B 12 and differ significantly from the present B₁₂ B 12 values.