Computergestützte und experimentelle Bestimmung der thermophysikalischen Eigenschaften von wasserstoffhaltigen Gasgemischen

The cross second virial coefficients B_12 for interactions of molecular nitrogen ­(N₂) with molecular hydrogen (H₂), of molecular oxygen (O₂) with H2, and of carbon dioxide (CO₂) with H₂ 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 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 ­ N2–H2 and ­ CO₂–H₂ systems are in excellent agreement with the most accurate experimental data. For the O₂–H₂ system, there are no experimental B_12 data because this mixture is highly explosive. There are, however, previous first-principles results for 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 B_12 and differ significantly from the present values.

In the project H2MIXPROP, highly accurate data for several thermophysical properties of gaseous mixtures containing molecular hydrogen are obtained by state-of-the-art theoretical approaches and experimental methods. Such data are required for many technical applications in the transition of the energy supply system to renewable energy sources, in which hydrogen is expected to play a prominent role. This contribution describes theoretical results for cross second virial coefficients of several binary mixtures, the development and validation of a path integral Monte Carlo code for the simulation of quantum gases, and the current status of the experimental tasks.