Fabrizio Esposito

Quasi-classical dynamics and vibrational kinetics of N+N2(v) system

Abstract Vibrational–translational (V–T) energy transfer and dissociation cross-sections of collisions of nitrogen atoms with rovibrationally excited nitrogen molecules are calculated by a quasi-classical dynamical approach. The results, relative to the whole set of vibrational states and interpolated on rotation, including quasi-bound levels, are used in a kinetic scheme for studying the global rate of dissociation. The kinetic model, which solves a system of 68 vibrational levels submitted to the action of V–T and dissociation processes, reveals some distortions in the resulting vibrational distribution function for v >40. The calculated global dissociation rate is in good agreement with the experimental results in a wide temperature range.

Non-equilibrium plasma kinetics: a state-to-state approach

State-to-state approaches are used to shed light on (a) thermodynamic and transport properties of LTE plasmas, (b) atomic and molecular plasmas for aerospace applications and (c) RF sustained parallel plate reactors. The efforts made by the group of Bari in the kinetics and dynamics of electrons and molecular species are discussed from the point of view of either the master equation approach or the molecular dynamics of elementary processes. Recent experimental results are finally rationalized with a state-to-state kinetics based on the coupling of vibrational kinetics with the Boltzmann equation for the electron energy distribution function.

Vibrational kinetics, electron dynamics and elementary processes in H2 and D2 plasmas for negative ion production: modelling aspects

We report current and past efforts made by our group in the ab initio modelling of different negative ion sources. In particular, we discuss the cross sections of elementary processes relevant to negative ion kinetics, including electron?molecule, atom?molecule and atom/molecule gas surface interactions, particularly emphasizing the role of vibrational excitation in affecting the cross sections. Attention is also paid to the elementary processes involving caesium in both volume and surface sources.Self-consistent models, which couple the Boltzmann equation and the vibrational kinetics, are used for describing multipole and rf discharges, while a PIC-MC (particle in cell) with Monte Carlo collisions is used to study electron and ion dynamics in a parallel plate reactor in the post-discharge regime. The present theoretical results should encourage further dedicated experimental work in the field.

Fundamental aspects of plasma chemical physics

Electron-molecule cross sections and rates involving rotationally, vibrationally and electronically excited states.- Reactivity and relaxation of vibrationally/rotationally excited molecules with open shell atoms.- Formation of vibrationally and rotationally excited molecules during atom recombination on surfaces.- Collisional-radiative models for atomic plasmas.- Collisional-radiative models for molecular plasmas.- Kinetic and Monte Carlo approaches to solve Boltzmann equation for the electron energy distribution functions.- Non-equilibrium plasma kinetics under discharge and post-discharge conditions: coupling problems for low pressure and atmospheric cold plasmas.- Ion transport under strong fields.- PIC (Particle In Cell ) models for low-pressure plasmas.- Negative ion H- for fusion.- Non equilibrium plasma expansion through nozzles.

Direct simulation of non-equilibrium kinetics under shock conditions in nitrogen

Abstract We study the interplay of vibrational kinetics, dissociation, translational and rotational relaxation in a strong shock wave in nitrogen by Direct Simulation Monte Carlo simulation (DSMC). The input data for vibrational and chemical processes are all in the form of cross-sections, mostly determined by molecular physics methods. In particular, we use for the first time very recent Quasi-Classical Trajectory (QCT) results for cross-sections of multi-quantum VT energy exchange and dissociation in N+N 2 collisions. Non-equilibrium distributions are observed and discussed.

Quasi-classical dynamics calculations and state-selected rate coefficients for H+H2(v,j)→3H processes: application to the global dissociation rate under thermal conditions

Abstract The quasi-classical trajectory method has been applied to the calculation of a complete set of cross-sections for the H+H2(v,j)→3H processes, using the LSTH potential energy surface. The results have been used to get the global dissociation rate of molecular hydrogen induced by atomic hydrogen, obtaining good agreement with experimental results.

Selective Vibrational Pumping of Molecular Hydrogen via Gas Phase Atomic Recombination

Formation of rovibrational excited molecular hydrogen from atomic recombination has been computationally studied using three body dynamics and orbiting resonance theory. Each of the two methods in the frame of classical mechanics, that has been used for all of the calculations, appear complementary rather than complete, with similar values in the low temperature region, and predominance of three body dynamics for temperatures higher than about 1000 K. The sum of the two contributions appears in fairly good agreement with available data from the literature. Dependence of total recombination on the temperature over pressure ratio is stressed. Detailed recombination toward rovibrational states is presented, with large evidence of importance of rotation in final products. Comparison with gas-surface recombination implying only physiadsorbed molecules shows approximate similarities at T = 5000 K, being on the contrary different at lower temperature.

Thermodynamics, Transport and Kinetics of Equilibrium and Non-Equilibrium Plasmas: A State-to-State Approach

Thermal non-equilibrium plasmas have been deeply investigated theoretically by means of the state-to-state approach, offering the unique opportunity of a detailed information about internal distributions affecting thermodynamics, transport coefficients and kinetics, properly accounting for the presence of excited states. The efforts made in the construction of knowledge on the dynamics of elementary processes occurring in the plasma with resolution on internal degrees of freedom, required by the method, are discussed. Boltzmann equation is solved for electrons self-consistently coupled to the chemical species collisional dynamics, reproducing very interesting features of strongly non-equilibrium internal distributions, characterizing plasmas.

Elementary processes and kinetics of H2 plasmas for different technological applications

Recent studies on elementary processes relevant to H2 plasmas are reviewed, emphasizing, in particular, vibrational state selected electron–molecule and heavy particle–molecule interactions. These data are then discussed in the framework of plasma kinetics for reactors of technological applications. Particular emphasis is given to microwave and parallel-plate RF discharges.

Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong non-equilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electron-impact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N2, O2, NO), Mars (CO2, CO, N2) and Jupiter (H2, He) atmospheres are considered.