Transport cross sections and collision integrals of atoms/ions: N-H⁺, H-N⁺, N²⁺-H, N⁺-H⁺ collisions.

The transport properties of atomic gases (for plasma science and aerothermodynamics) are described by the properties of the relevant elastic collisions. Depending on the approach taken, a various quantities are used: the potential energy curves (molecular dynamics), transport cross sections (DSMC - Direct Simulation Monte Carlo, PIC-MCC - Particle In Cell Monte Carlo Collisions) or collision integrals (CFD - computational fluid dynamics). In most cases such data are not available or are calculated with very significant approximations.

The limitation is the availability of the potential energy curves (which can be numerous), especially for atoms/ions in the excited states. The present work reports potential energy curves for the N-H⁺, H-N⁺, N²⁺-H, N⁺-H⁺ interactions and calculated transport cross sections and collision integrals. The classical mechanics is shown (by comparison to the semiclassical WKB method) to be usually sufficient for the temperatures relevant to ionized gas regime; especially when the excellent performance of the classical mechanics in case of repulsive curves is taken into account. The extrapolation of potentials for higher energies (up to 1keV) is also discussed.

The usefulness of the following approximations will be discussed: use of exponential function for description of repulsive potentials, polarizability approximation for atom-ion interactions, and screened Coulomb potential for ion-ion interactions.

The collision integrals, transport cross sections and potential energy curves are available as supplementary material of publications. Transport cross sections are also stored in the CollisionDB database of IAEA.