Comparisons are made between potential energy surfaces (PESs) for N2 N and N2 N2 collisions and between rate coefficients for N2 dissociation that were computed using the quasi-classical trajectory (QCT) method on these PESs. For N2 N, 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 N2 N2, 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 N4 but give similar results. Thermal N2 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.
Bibliographical noteFunding Information:
During the last decade, there has been a major effort sponsored by NASA and the U.S. Air Force Office of Scientific Research (AFOSR) to develop new models for Earth entry based on the results of computational physics and chemistry research. This so-called physics-based modeling of hypersonic flows is predicated on the
R. L. Jaffe and D. W. Schwenke were supported by the NASA Space Technology Mission Directorate Entry Systems Modeling program. M. Grover was supported by a Doctoral Dissertation Fellowship at the University of Minnesota. T. E. Schwartzentruber and P. Valentini were supported by the AFOSR under grant FA9550-16-1-0161. M. Panesi and S. Venturi were supported by NASA under grant NNX15AQ57A. M. Grover and S. Venturi would like to thank Michael Barnhardt and David Hash at NASA Ames Research Center for providing internship opportunities and for encouraging the opportunity for collaboration between the University of Minnesota, the University of Illinois Urbana-Champaign, and Ames Research Center.