Comparison of Potential Energy Surface and Computed Rate Coefficients for N2 Dissociation

Abstract

Comparisons are made between potential energy surfaces (PES) for N 2 + N and N 2 + N 2 collisions and between rate coefficients for N 2 dissociation that were computed using the quasiclassical trajectory method (QCT) on these PESs. For N 2 + N we compare the Laganà's empirical LEPS surface with one from NASA Ames Research Center based on ab initio quantum chemistry calculations. For N 2 + N 2 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 N 4 , but give similar results. Thermal N 2 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

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N2–N System

“…As a result, the DMS method has been used successfully to study molecule−molecule interactions. [62][63][64]67 In the StS-ME approach, the generation of the kinetic database is the most time-consuming part. However, once this database exists, it can be reused indefinitely to solve eqs 3 and 4 or other problems given suitable initial conditions.…”

“…This means that no cross section or rate coefficient database needs to be compiled, and the required storage space and computer memory is moderate. As a result, the DMS method has been used successfully to study molecule–molecule interactions. − , …”

“…As part of a study of rovibrational coupling in nitrogen, the DMS method has been validated against full molecular dynamics (MD) calculations . With the increasing availability of highly accurate ab initio potentials from NASA Ames − and the University of Minnesota, − the DMS method has been used to study coupled rotational-vibrational energy exchange and dissociation in nitrogen ,− and oxygen , mixtures.…”

Bayesian Machine Learning Approach to the Quantification of Uncertainties on Ab Initio Potential Energy Surfaces

“…Recently, the authors of this paper made a first attempt in validating the PESs for N 2 + N and N 2 + N 2 from NASA Ames 14, 26 and the surface for N 2 + N 2 from University of Minnesota 6 by comparing thermal and quasisteady-state (QSS) 27 dissociation rates to shock-tube experiments. 28 The good agreement between the ab initio calculations and the experimental data justifies the need for the use of highfidelity first-principles approaches. However, while the results from these two previous studies suggest a not negligible sensitivity to the accuracy of the PES, a more systematic framework is necessary to quantify the uncertainty associated with the ab initio-based methodology and its potential impact on the nonequilibrium kinetics.…”

Analysis of Shockwave Radiation Data in Nitrogen

“…While these improvements were made with a small number of adjustable parameters, it is desirable to remove confounding effects created by the complexity of the mixture under study by examining a simpler system such as molecular nitrogen. At the same time, there has been a significant amount of theoretical work on molecular nitrogen using ab initio methods such as DMS and QCT [5][6][7][8]. These works have shown good agreement with current practices in nitrogen dissociation rates, but have cast doubts on modelling parameters such as vibrational relaxation times, Boltzmann modelling of vibrational states, and the influence of atomic collision partners on dissociation rates.…”