Comparison of Potential Energy Surface and Computed Rate Coefficients for Dissociation

Abstract

Comparisons are made between potential energy surfaces (PESs) for and collisions and between rate coefficients for dissociation that were computed using the quasi-classical trajectory (QCT) method on these PESs. For , Laganà’s empirical London–Eyring–Polanyi–Sato surface is compared with one from NASA Ames Research Center based on ab initio quantum chemistry calculations. For , two ab initio PESs (from NASA Ames and from the University of Minnesota) are compared. These use different methods for computing the ground state electronic energy for but give similar results. Thermal dissociation rate coefficients, for the 10,000–30,000 K 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 method (DMS) 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. It is concluded 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.