Comparison of quantum mechanical and empirical potential energy surfaces and computed rate coefficients for N₂ dissociation

Comparisons are made between potential energy surfaces (PES) for N₂ + N and N₂ + N₂ collisions and between rate coefficients for N₂ dissociation that were computed using the quasiclassical trajectory method (QCT) on these PESs. For N₂ + N we compare the Laganà’s empirical LEPS surface with one from NASA Ames Research Center based on ab initio quantum chemistry calculations. For N₂ + N₂ we compare two ab initio PESs (from NASA Ames and from the University of Minnesota). These use different methods for computing the ground state electronic energy for N₄, but give similar results. Thermal N₂ dissociation rate coefficients, for the 10,000K-30,000K temperature range, have been computed using each PES and the results are in excellent agreement. Quasi-stationary state (QSS) rate coefficients using both PESs have been computed at these temperatures using the Direct Molecular Simulation of Schwartzentruber and coworkers. The QSS rate coefficients are up to a factor of 5 lower than the thermal ones and the thermal and QSS values bracket the results of shock-tube experiments. We conclude that the combination of ab initio quantum chemistry PESs and QCT calculations provides an attractive approach for the determination of accurate high-temperature rate coefficients for use in aerothermodynamics modeling.