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Description
In order to represent the interactions between particles composing chemical systems of practical interest for the hypersonic community, such as N2 + N [1], CO + O and O2 + C [2], and O2 + O [3], during the last decade a variety of Potential Energy Surfaces (PESs) has been computed starting from the first principle of quantum physics. The accuracy of these potentials, together with the computational efficiency of recent codes implementing Quasi Classical Trajectory method (QCT) for calculating inelastic, dissociation and exchange rate coefficients, are making possible a detailed analysis of the ro-vibrational state-to-state non-equilibrium kinetic processes, and are highlighting dynamics and behaviors that a mere vibrational specific methodology would tend to hide or to misinterpret. This work presents the authors’ new findings concerning the importance of the rotational component in the diatoms’ excitation and dissociation processes, which resulted from the examination of an extensive database of ro-vibrational rate coefficients and 0-D simulations for the four systems mentioned above. Gephi [5], a software for social and biological network visualization, has been used for understanding the connectivities and analyzing the links between the molecules’ quantum states: in agreement with the results of Sahai’s algorithm for grouping N2 levels [6], the states characterized by low rotational energy (J < 80) appeared to be strongly connected to the ones sharing the same vibrational state; for levels with higher J, however, the larger the rotational contribution to the molecule’s energy, the more isotropic in the quantum numbers space such connections tended to be. Moreover, the preferential channels for exciting the high-lying energy states presented the same structures in all the diatoms analyzed by the authors so far; this fact motivates the very similar excitation dynamics that has been noticed when heath bath simulations have been performed in different chemical systems (Fig. 1). Rotation has also shown to have a crucial role in the molecule’s dissociation: a strong positive correlation has been found between the energy-distance of a ro-vibrational state from the centrifugal barrier and its specific dissociation rate (Fig. 2).
REFERENCES
1. Jaffe, R. et al. Vibrational and Rotational Excitation and Relaxation of Nitrogen from Accurate Theoretical Calculations,
46th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, 2008.
2. Schwenke, D. W. et al. Collisional Dissociation of CO: ab initio Potential Energy Surfaces and Quasiclassical Trajectory
Rate Coefficients, NASA Report 20160012461, 2016.
3. Varga, Z. et al. Potential energy surfaces for O+O2 collisions, The Journal of Chemical Physics 138, 2013.
4. Panesi, M. et al. Rovibrational internal energy transfer and dissociation of N2(1Σg+)-N(4S(u)) system in hypersonic
flows, The Journal of Chemical Physics 138, 2013.
5. Bastian M., et al. Gephi: an open source software for exploring and manipulating networks, International AAAI Conference
on Weblogs and Social Media, 2009.
6. Sahai, A. et al. Adaptive coarse graining method for energy transfer and dissociation kinetics of polyatomic species,
The Journal of Chemical Physics 147, 2017.
7. Colonna, G. et al. The Role of Rotation in State-to-State Vibrational Kinetics, 9th AIAA/ASME Joint Thermophysics
and Heat Transfer Conference, San Francisco, California, 2001.
Summary
This work presents the authors’ new findings concerning the importance of the rotational component in the diatoms’ excitation and dissociation processes, which resulted from the examination of an extensive database of ro-vibrational rate coefficients and 0-D simulations for 4 chemical systems of high interest in Hypersonics community.
