A Database of Transport Cross Sections for Planetary Atmospheres

The new impulse to the solar system exploration, testified by the planned NASA missions to the Ice Giants [1], i.e. Neptune and Uranus, is triggering the theoretical activity on the modeling of the hypersonic entry in the planets' atmospheres. In this context it is relevant to characterize the thermodynamics and transport properties of the plasma formed in the shock layer, also accounting on the role of chemical species ablated from the carbon phenolic thermal protection systems. For the accurate estimation of thermodynamic properties and transport coefficients, here the webaccess tool EquilTheTA (EQUILibrium for plasma THErmodynamics and Transport Applications) [2] is exploited. The tool, stable and reliable in wide temperature and pressure ranges, derives the quantities from core databases of atomic and molecular energy levels and collision integrals, in the frame of the classical theory of statistical thermodynamics and the Chapman-Enskog theory, respectively. The creation of a complete database of transport cross sections for binary heavy-particle interactions in complex mixtures including large number of species has been successfully tackled adopting a hybrid approach [3] that combines the traditional multi-potential with the phenomenological approach [4]. In the multi-potential approach, the effective collision integrals for a given interaction results from the averaging procedure of terms corresponding to each allowed interaction between the two colliding partners, while the phenomenological approach is very attractive, allowing the derivation of complete and consistent datasets of collision integrals for any interaction, estimating the interaction potential on a physically sound basis. In fact, the average interaction is modeled by an Improved Lennard Jones (ILJ) potential, whose features (depth and position of the well) are derived by correlation formulas given in terms of fundamental physical properties of interacting partners (dipole polarizability, charge, number of electrons effective in polarization). These approaches, combined with the asymptotic approach for the estimation of the resonant chargeexchange contribution to odd-order collision integrals, represent a powerful strategy to extend the collision integral database. The transport cross sections for the matrix of binary interactions involving chemical species relevant to the H2/He/C/H system are derived, including molecules, molecular ions, neutral and ionized atoms, so as to fully describe the low temperature, dissociative and ionization regimes of the plasma.