Role of dissociative recombination in the excitation kinetics of an argon microwave plasma at atmospheric pressure

Abstract

A collisional radiative model was developed in order to investigate the influence of dissociative recombination on the Saha–Boltzmann plasma equilibrium. As the dissociative recombination products are not well known, their relative importance was tested through comparison with the distribution of line intensities obtained in a microwave argon discharge produced at atmospheric pressure by a surface wave. It was found that the main dissociation products are the ground state and the 4s levels, the 5p and upper levels playing a negligible role. Because the higher levels are only weakly affected by dissociative recombination, they remain in partial local thermodynamic equilibrium. Therefore, the excitation temperature determined from these levels adequately describes the electron temperature. The model well reproduces experimental measurements of excitation temperature, rotational temperature, electron density, and absolute populations of the excited levels.

Time resolved optical emission spectroscopy in power modulated atmospheric pressure plasma jet

“…The often used assumption of partial Local Thermodynamic Equilibrium (pLTE) means that top atomic levels obey the Saha equation and Boltzmann statistics. In that case the excitation temperature (T exc ) derived from the Boltzmann plot [19] should be equivalent to the electron temperature [20][21][22]. Some authors [23] have used a direct but experimentally challenging technique of Thomson scattering to determine the electron temperature.…”

Single channel atmospheric pressure transporting plasma and plasma stream demultiplexing: physical characterization and application toE. colibacteria inactivation

“…In low temperature plasmas, the excitation temperature (T exc ) derived from the Boltzmann plot [38] should be equivalent to the electron temperature (T e ) [39][40][41]. T exc for the transporting discharge has been determined from the emission intensities of helium lines.…”

On the kinetic and thermodynamic electron temperatures in non-thermal plasmas

“…(12). In order to check the relation between both temperatures in a more general context, we have solved the homogeneous steadystate Boltzmann equation in the two terms Legendre expansion approximation [8] using the software BOLSIG [26][27].…”

“…These are results from some selected papers in the literature, but there are numerous evidences of this behavior in many situations (see for instance refs. [12][13][14][15][16][17] and references therein). The existence of this balance is explained by considering the high interaction rate between free electrons and higher-lying excited states, caused by the low energy threshold for electron-induced collisional ionization/recombination processes [18].…”

“…From an experimental point of view, there are numerous evidences of the abovementioned ionization-recombination balance with free electrons, mostly thanks to optical emission spectroscopy data collected from radiative decays of upper excited states of neutral particles in plasmas produced at the laboratory: in reference [12], for instance, a microwave argon discharge at atmospheric pressure was analyzed finding that the relation   /1 SB pp nn holds when 3 p  . Also, in reference [13] the thermal inequilibrium of a non-thermal, atmospheric helium microwave plasma was studied through optical emission spectroscopy, obtaining that the population density of neutral particles excited states also followed Eq.…”