Kinetic study of low-temperature CO₂plasmas under non-equilibrium conditions. I. Relaxation of vibrational energy

Abstract

A kinetic model describing the time evolution of ∼70 individual CO 2 (X 1 Σ + ) vibrational levels during the afterglow of a pulsed DC glow discharge is developed in order to contribute to the understanding of vibrational energy transfer in CO 2 plasmas. The results of the simulations are compared against in situ Fourier transform infrared spectroscopy data obtained in a pulsed DC glow discharge and its afterglow at pressures of a few Torr and discharge currents of around 50 mA. The very good agreement between the model predictions and the experimental results validates the kinetic scheme considered here and the corresponding vibration-vibration and vibration-translation rate coefficients. In this sense, it establishes a reaction mechanism for the vibrational kinetics of these CO 2 energy levels and offers a firm basis to understand the vibrational relaxation in CO 2 plasmas. It is shown that first-order perturbation theories, namely, the Schwartz-Slawsky-Herzfeld and Sharma-Brau methods, provide a good description of CO 2 vibrations under low excitation regimes.

The case forin situresource utilisation for oxygen production on Mars by non-equilibrium plasmas

“…n correspond to the quanta of vibration in the symmetric stretching, bending and asymmetric stretching modes, respectively-were measured by IR absorption [16,17] and calculated from a detailed self-consistent kinetic model accounting for e-V, V-T and V-V transfers involving ∼70 vibrational levels [18,19], whose predictions are in excellent agreement with the experimental results. Herein, the model developed in [18,19], where the selfconsistent coupling between the electron and vibrational kinetics is made as described in [20], is used to assess the capability of non-equilibrium plasmas to efficiently up-pump CO 2 vibrational quanta in Martian conditions. For this purpose, we focus on a DC pulsed discharge operating at discharge current I=50mA, pulse length t 5 D = ms and gas pressure p=5Torr, corresponding to one of the conditions on Earth reported in [16,18] and to the relevant pressure on Mars.…”

“…Pulsed DC discharges constitute an ideal system for fundamental studies, since their simple geometry and homogeneity makes them accessible to a series of diagnostics and suitable for the development of 0D self-consistent kinetic models, accounting for very complex vibrational and chemical kinetics. CO 2 pulsed discharges have been very recently investigated, both experimentally [16,17] and theoretically [18,19], for a Pyrex cylindrical plasma reactor (23cm length, 2 cm diameter), operated under flowing conditions in the millibar range, with a pulsed 10-50mA plasma current at 5/10ms on/off. In particular, the time-resolved populations of the vibrational levels…”

Introductory Chapter: Plasma Chemistry for Better CO2 Conversion

“…Motivated by the previously mentioned strategy, numerous research groups are currently focused on achieving the maximum conversion and energy efficiencies (defined in the following chapters) associated to the CO 2 decomposition via modeling [10,11] as well as through the experimental studies [12][13][14][15]. In addition to the plasma itself, utilization of the pre-activated highly porous catalyst may also significantly increase the energy efficiency of the conversion process, as shown in the numerous literature sources [16,17] and demonstrated in this book.…”

“…Under this scenario, it is possible to benefit from the energy stored in the vibrational levels, that is, vibrational excitation of the molecule, which is known to be favorable for molecular decomposition in the case of CO 2 [6]. More specifically, if the electron energy is selectively channeled into the CO 2 asymmetric stretch mode of vibration, then the vibrational quanta can be pumped up through the so-called vibrational "ladder climbing" mechanism, offering a unique way to achieve efficient decomposition [10].…”

Rate Coefficients of Exchange Reactions in Air and Carbon Dioxide

“…Другой важной проблемой является полное отсутствие данных траекторных расчетов для поуровневых коэффициентов скоростей реакции в CO2, что не дает возможности провести надежную валидацию теоретических моделей. Тем не менее, в последнее время появилась большая потребность в теоретических моделях поуровневых обменных реакций для моделирования как высокотемпературных процессов при входе в атмосферу Марса [19,20,21], так и низкотемпературных плазмохимических процессов в экспериментах по конверсии углекислого газа [22,23,24,25]. В работе мы предлагаем обобщение модели, разработанной для обменных реакций в воздухе, и первые результаты расчетов.…”