The hypersonic entry of meteoroids into Earth's atmosphere induces ablation with the production of molecular and atomic species in the environment. The formed species are subjected to the action of several collision processes, including electron- molecule and heavy-particle-heavy-particle collisions. The high level of gas temperature achieved by the medium promotes reactive channels which can be aided by the presence of vibrationally excited states in either the flow or in the boundary layer surrounding the meteoroid. The characterization of the relevant processes requires, in particular, the dependence of cross sections and rate coefficients on the vibrational quantum number of the reactants. This dependence has been extensively studied in the case of electron-molecule processes (see chapter 15), while the corresponding behavior of heavy-particle-heavy-particle reactive collisions is still an unsolved problem so that their characterization still requires the use of simplified methods. The aim of this chapter is to present the application of an old but still widely used method to analyze the reactive channels promoted by gas temperature and vibrational temperature and their role in affecting the properties of the whole medium excited during the meteoroid impact. We select, in this case, a plasma formed in the activation of both CO2 and CO molecular species and their influence on the whole kinetics. These species are produced during the ablation of selected meteoroids (see chapter 6) [1]. The plasma kinetics code to understand the role of vibrational excitation in promoting bimolecular reactions, developed in the last few years by some of the current authors, has been used to this end. A second case study considers the activation of the different processes by an instantaneous increase of gas temperature followed by the formation of well-structured vibrational distribution functions and the opening of reactive channels aided by this excitation. The chapteris essentially divided in two parts, the first dedicated to the state-to-state rates in molecular collisions, while the second examines the use of these rates in modeling the global rates of reactive processes involving heavy-particle collisions as compared to the corresponding rates promoted by electron-impact collisions. In the first part, particular emphasis is given to the Boudouard reaction rates and to the dissociation rates, which are strongly assisted by the presence of vibrational excitation of the medium. Different plasma kinetics are discussed in the second part, emphasizing situations where non-equilibrium vibrational distributions and non-equilibrium electron energy distribution functions play an important role in affecting the rate coefficients of reactive processes.
The role of vibrational activation and bimolecular reactions in non-equilibrium plasma kinetics
Pietanza Lucia Daniela;Capitelli Mario;Colonna Gianpiero;
2019
Abstract
The hypersonic entry of meteoroids into Earth's atmosphere induces ablation with the production of molecular and atomic species in the environment. The formed species are subjected to the action of several collision processes, including electron- molecule and heavy-particle-heavy-particle collisions. The high level of gas temperature achieved by the medium promotes reactive channels which can be aided by the presence of vibrationally excited states in either the flow or in the boundary layer surrounding the meteoroid. The characterization of the relevant processes requires, in particular, the dependence of cross sections and rate coefficients on the vibrational quantum number of the reactants. This dependence has been extensively studied in the case of electron-molecule processes (see chapter 15), while the corresponding behavior of heavy-particle-heavy-particle reactive collisions is still an unsolved problem so that their characterization still requires the use of simplified methods. The aim of this chapter is to present the application of an old but still widely used method to analyze the reactive channels promoted by gas temperature and vibrational temperature and their role in affecting the properties of the whole medium excited during the meteoroid impact. We select, in this case, a plasma formed in the activation of both CO2 and CO molecular species and their influence on the whole kinetics. These species are produced during the ablation of selected meteoroids (see chapter 6) [1]. The plasma kinetics code to understand the role of vibrational excitation in promoting bimolecular reactions, developed in the last few years by some of the current authors, has been used to this end. A second case study considers the activation of the different processes by an instantaneous increase of gas temperature followed by the formation of well-structured vibrational distribution functions and the opening of reactive channels aided by this excitation. The chapteris essentially divided in two parts, the first dedicated to the state-to-state rates in molecular collisions, while the second examines the use of these rates in modeling the global rates of reactive processes involving heavy-particle collisions as compared to the corresponding rates promoted by electron-impact collisions. In the first part, particular emphasis is given to the Boudouard reaction rates and to the dissociation rates, which are strongly assisted by the presence of vibrational excitation of the medium. Different plasma kinetics are discussed in the second part, emphasizing situations where non-equilibrium vibrational distributions and non-equilibrium electron energy distribution functions play an important role in affecting the rate coefficients of reactive processes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
