Comparison of potential energy surfaces and computed rate coefficients for N dissociation.

Comparisons are made between potential energy surfaces (PES) for N + N and N + N collisions and between rate coefficients for N dissociation that were computed using the quasiclassical trajectory method (QCT) on these PESs. For N + N we compare the Laganà's empirical LEPS surface with one from NASA Ames Research Center based on quantum chemistry calculations. For N + N we compare two PESs (from NASA Ames and from the University of Minnesota). These use different methods for computing the ground state electronic energy for N, but give similar results. Thermal N 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 quantum chemistry PESs and QCT calculations provides an attractive approach for the determination of accurate high-temperature rate coefficients for use in aerothermodynamics modeling.