Optical emission study of nonthermal plasma confirms reaction mechanisms involving neutral rather than charged species

Abstract

Charge transfer reactions are commonly used to explain NO x conversion in nonthermal plasma. An analysis of optical emission spectra induced by pulsed corona discharge in NO x-containing argon suggests that, in fact, the contribution of charge transfer reactions to NO x conversion in nonthermal plasma is negligible. During electrical discharge in such gas mixtures, NO͑B͒, an electronic excited state of NO formed due to the dissociative recombination reactions of NO 2 + and N 2 O + and the optical emission of NO͑B͒ could be a proof that cations are responsible for NO x conversion. However, the optical emission of NO͑B͒ is not observed, leading to the conclusion that cations are not involved to any measurable degree. Therefore, charge transfer reactions cannot play a significant role in nonthermal plasma largely because the cations are neutralized with electrons before any charge transfer reactions can occur and concentrations of radicals are far higher than those of cations, which inhibits charged particle reactions. Instead, neutral active species, such as atoms, molecular fragments, and excited molecules, are the major active species contributing to nonthermal plasma reactions.

Room-temperature atmospheric argon plasma jet sustained with submicrosecond high-voltage pulses

“…3, much smaller than that in atmospheric argon jets reported so far. 26 These are much stronger in the pulsed case with the intensity ratio of the pulsed-to-sine cases being 1.85, 1.74, and 3.33 for the three strongest Ar lines at 696.5, 763.5, and 811.5 nm. The pulsed-to-sine intensity ratio for the atomic oxygen line at 777 nm is similarly large at 3.3.…”

Novel Composite Hydrogen-Permeable Membranes for Nonthermal Plasma Reactors for the Decomposition of Hydrogen Sulfide

“…The first two principal peaks for orthorhombic αsulfur were observed in the X-ray diffraction data. (3) As shown in our recent investigation, 44 the degree of ionization in the pulsed corona discharge is low. The major active species are produced through electron collision in the streamers, whose total volume is 10 -4 -10 -3 of the reactor volume.…”

“…35 In the streamer head, the concentration of ions (corresponding to concentration of electrons) is around 15 ppm. 44 Conversion of H 2 S through pathways (III) and (IV) can be supported by the following points:…”

“…24 Ma et al 25 and Helfritch 21 proposed that the H 2 S conversion mechanism in any of these gases involves ionization of H 2 S (e + H 2 S → H 2 S + + 2e ) and subsequent charge neutralization with dissociation (H 2 S + + e → HS + H). Abolentsev et al 1 proposed an alternate three step mechanism for H 2 S conversion: (1) 44 showed that ionization reactions in nonthermal plasmas are negligible.…”

Study on the Reaction of CCl2F2with CH4in a Dielectric Barrier Discharge Nonequilibrium Plasma

“…The presence of metastable argon atoms in the non‐thermal plasma has been examined by several researchers through the observation and analysis of optical emission spectra and most researchers suggest that these species are present in a significant quantity and contribute to the reactions occurring. These atoms are produced by collision of neutral argon atoms with fast electrons or from the radiative recombination of argon ions with slow electrons …”