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

Abstract The cross second virial coefficients $$B_{12}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mn>12</mml:mn> </mml:msub> </mml:math> 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. $$B_{12}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mn>12</mml:mn> </mml:msub> </mml:math> 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 $$B_{12}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mn>12</mml:mn> </mml:msub> </mml:math> data because this mixture is highly explosive. There are, however, previous first-principles results for $$B_{12}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mn>12</mml:mn> </mml:msub> </mml:math> 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 $$B_{12}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mn>12</mml:mn> </mml:msub> </mml:math> and differ significantly from the present $$B_{12}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mn>12</mml:mn> </mml:msub> </mml:math> values.