Ab initio state-specific N2 + O dissociation and exchange modeling for molecular simulations

Abstract

Quasi-classical trajectory (QCT) calculations are used in this work to calculate state-specific N(XΣ)+O(P)→2N(S)+O(P) dissociation and N(XΣ)+O(P)→NO(XΠ)+N(S) exchange cross sections and rates based on the 1A″ and 1A' ab initio potential energy surface by Gamallo et al. [J. Chem. Phys. 119, 2545-2556 (2003)]. The calculations consider translational energies up to 23 eV and temperatures between 1000 K and 20 000 K. Vibrational favoring is observed for dissociation reaction at the whole range of collision energies and for exchange reaction around the dissociation limit. For the same collision energy, cross sections for v = 30 are 4 to 6 times larger than those for the ground state. The exchange reaction has an effective activation energy that is dependent on the initial rovibrational level, which is different from dissociation reaction. In addition, the exchange cross sections have a maximum when the total collision energy (TCE) approaches dissociation energy. The calculations are used to generate compact QCT-derived state-specific dissociation (QCT-SSD) and QCT-derived state-specific exchange (QCT-SSE) models, which describe over 1 × 10 cross sections with about 150 model parameters. The models can be used directly within direct simulation Monte Carlo and computational fluid dynamics simulations. Rate constants predicted by the new models are compared to the experimental measurements, direct QCT calculations and predictions by other models that include: TCE model, Bose-Candler QCT-based exchange model, Macheret-Fridman dissociation model, Macheret's exchange model, and Park's two-temperature model. The new models match QCT-calculated and experimental rates within 30% under nonequilibrium conditions while other models under predict by over an order of magnitude under vibrationally-cold conditions.

Accurate reproducing kernel-based potential energy surfaces for the triplet ground states of N2O and dynamics for the N + NO ↔ O + N2and N2+ O → 2N + O reactions

“…33 and 68. The parameters for the present fits are given in Table 2 and all fits agree well except at high temperatures for which the fit from ref. 68 gives a higher dissociation rate.…”

“…26 yield reaction rates for the forward and reverse process in good agreement with experiment. 26,[31][32][33]68 further suggests that these PESs have certain deficiencies only in the long range part because for reactive processes the short range, strongly interacting region is primarily relevant. As the VR rates from the present analysis agree qualitatively with experiment over the entire temperature range, the present PESs are a good starting point for further improvements on the shape of the PESs.…”

Prediction of Flight Measurements of High-Enthalpy Nonequilibrium Flow from a CubeSat-Class Atmospheric Probe

“…A newly considered reaction rate that is derived from quasi-classical trajectory (QCT) rates similar to the rates developed by Bose and Candler [17] is also shown from the work of Luo et al [13]. The rates calculated by Luo et al are similar to the rates of Park and Baulch at lower temperatures, but predict higher rates of NO formation for both temperatures simulated, T t = 10000K and T t = 8000K, which can be seen clearly from Fig. 14(a) in Ref [13]. Despite the change in rates, the final concentration of the species is still the same because the equilibrium state is determined by the processes considered.…”

Master equation simulation of O2-N2 collisions on an ab-initio potential energy surface

“…from nitrogen to oxygen. Equations (14) and (15) describe the simultaneous vibrational deactivation of oxygen and nitrogen. While such energy transfer is less probable than the processes, given by Eqs.…”

“…The initial capacity for such research was formed by the ever-increasing computational power such that statistical methods became tractable as well as by the variety of potential energy surfaces (PES), developed for studies of low temperature kinetics in the upper atmosphere. [1][2][3][4] While a large amount of previous work regarding the nonequilibrium processes in high temperature gases has concentrated on the state-resolved chemistry of nitrogen [5][6][7][8][9] and nitric oxide [10][11][12][13][14] due to the importance of these species in re-entry and combustion problems, thermochemistry of oxygen has received less attention. This is due to the fact that the atmosphere contains only 0.2 molar fraction of oxygen, and it dissociates easily under harsh re-entry conditions.…”