Search

This work proposes a complete and consistent set of cross sections for electron impact collisions with carbon monoxide (CO), to be published in the IST-Lisbon database with LXCat. The set is validated by comparing swarm parameters calculated using the two-term Boltzmann solver LoKI-B with available experimental data. A severe inconsistency between the total rotational and effective cross sections reported in the literature for low values of the electron energy (ϵ < 0.1 eV) is pointed out. It is shown that inelastic and superelastic collisions involving rotationally excited levels, as well as superelastic collisions with the first vibrational excited level, have to be taken into account to accurately calculate the electron energy distribution function. The relevance of these mechanisms implies a dependence of the effective momentum transfer cross section on the gas and vibrational temperatures and suggests its replacement by an elastic momentum transfer cross section. The electron kinetics in CO2–CO mixtures are also discussed in detail, namely the influence of vibrational excitation and of the CO2/CO ratio on the electron energy distribution function, rate coefficients and power transfer. The vibrational temperatures of both CO and the different vibrational modes of CO2 have a marked influence on the results, due to the importance of superelastic collisions with the vibrationally excited states of both gases. The presence of CO in the mixture modifies the energy transfer pathways and, at moderate reduced electric fields (∼30−100 Td), the vibrational excitation of CO can become the dominant energy loss mechanism, affecting the input of electron energy into the asymmetric stretching mode of CO2. [ABSTRACT FROM AUTHOR]

This paper reviews the basics of kinetic modelling in low-temperature N2–O2 plasmas, including the strong coupling between electron, vibrational, chemical and surface kinetics. The main approaches to investigate each of these kinetics are outlined and the most widely used ones are discussed in some detail. The interdependency of the different kinetics is also considered. In such a formulation, the building blocks of kinetic models in molecular plasmas are the electron Boltzmann equation, a system of rate balance equations describing the creation and loss of the most important neutral and charged heavy-particles, including the relevant vibrationally excited states and all vibration energy transfers, a proper description of transport of charged particles, and a description of heterogeneous particle destruction and molecule formation. All the details required to build a model for N2–O2 plasmas are given either explicitly or by indicating relevant references, so that the interested reader has all the necessary information to build a similar model. Some new calculations are presented to illustrate and study a few specific phenomena, including the electron power transfer in air plasmas, the formation of the vibrational distribution function in O2 dc discharges, the calculation of gas heating in pulsed air plasmas, and the heterogeneous formation of ozone in an oxygen afterglow. Finally, some open challenges and directions for further research are pointed out. [ABSTRACT FROM AUTHOR]

This paper studies two linear resonator sources, which use a continuous 2.45-GHz microwave excitation to produce stable microplasmas, in air and in argon, at atmospheric pressure. The discharges are produced and sustained within the 50-200-μm gap created between two metal electrodes with either 6 or 14 mm in length. Particular attention is given to the design and optimization of the sources (in terms of frequency tuning and power coupling), following a complementary approach based on simulations and experiments. Optical-emission-spectroscopy diagnostics allow one to deduce the rotational, vibrational, and excitation gas temperatures and the electron density (using Stark broadening measurements of the Hβ line-emission profile). [ABSTRACT FROM AUTHOR]

This paper analyzes the formation of double space-charge sheaths, associated to the development of double ionization structures in radio frequency discharges. A simulation tool is used to generate space-time images of the ionization rate in hydrogen and in helium, obtained by inducing artificial modifications in the mobility of charged particles, with these gases. [ABSTRACT FROM AUTHOR]

This work presents a detailed investigation aimed at understanding the key mechanisms governing nitric oxide (NO) production in N 2 -O 2 discharges by systematically comparing experimental results to modeling data. The experimental phase capitalizes on radiofrequency (13.56 MHz) discharges, sustained at 5 mbar pressure conditions, featuring varying concentrations of oxygen, ranging from pure N 2 plasma to air-like mixtures. On the modeling front, we adopt an integrated approach that combines the solution of the Boltzmann equation for electrons with a system of rate balance equations for heavy species. To account for ground state NO(X) generation at the reactor wall, we combine the volume chemistry with a mesoscopic description of the surface, taking into account adsorption sites and various elementary surface phenomena. Comparisons between experiments and modeling demonstrate very good agreement, extending beyond NO(X) formation to encompass other species in the plasma such as N 2 O(X) and atomic nitrogen N( 4 S). Noteworthy findings include (i) the pivotal role of surface mechanisms in NO(X) production, particularly at low oxygen content values; (ii) the significance of accurately describing the postdischarge phase, where depletion of plasma species occurs at different time scales (millisecond range); and (iii) the importance of vibrationally and electronically excited states (e.g., O 2 (b)) in elucidating NO(X) formation dynamics, crucial for unraveling reaction pathways and energy transfer processes. This work makes an important step toward formulating a comprehensive reaction mechanism for N 2 and N 2 -O 2 plasmas applied to nitrogen fixation, covering both volume and surface mechanisms, and lays a robust foundation for future research on plasma-based NO(X) production, particularly in the presence of catalysts.