Ar-N₂O Microwave Plasmas and Afterglows Sustained at Atmospheric Pressure

Abstract

In this study, Ar–N2O discharges sustained by a surfatron device operated at atmospheric pressure were investigated to elucidate their physicochemical behavior and potential for reactive oxygen and nitrogen species (RONS) generation through N2O decomposition. The addition of N2O to an argon plasma led to a shortening of the plasma column and the appearance of a diffuse afterglow region that extends to long distances (> 50 cm). Increasing concentration results in suppression of the discharge filamentation, as well as to an increase in gas temperature, that exceeds 3000 K above 1.5% N2O. Spectroscopic and thermometric analyses confirmed effective N2O dissociation and the formation of RONS in the discharge. The afterglow, characterized by long-lived metastables and excited argon, nitrogen, and oxygen species, exhibited progressively decreasing temperatures, reaching below 100 °C. Optical emission analysis in this zone revealed rich Ar, N, O, NO, OH, and NH spectra, from which dissociation pathways and kinetic mechanisms have been proposed. A simplified kinetics scheme to elucidate the behavior of these plasmas is proposed, and the results are compared to those obtained with Ar–N2 plasmas and postdischarges. In addition, mass spectrometry suggests N2O decomposition preferentially takes place through nitrogen-oxygen bond breaking, yielding N2, O2, and NOx products at the gas exhaust.