Contribution of Discharge Excited Atomic N, N₂*, and N₂⁺ to a Plasma/Liquid Interfacial Reaction as Suggested by Quantitative Analysis

Electric-discharge nitrogen comprises three main types of excited nitrogen species-atomic nitrogen (Natom ), excited nitrogen molecules (N₂ *), and nitrogen ions (N₂⁺ ) - which have different lifetimes and reactivities. In particular, the interfacial reaction locus between the discharged nitrogen and the water phase produces nitrogen compounds such as ammonia and nitrate ions (denoted as N-compounds generically); this is referred to as the plasma/liquid interfacial (P/L) reaction. The Natom amount was analyzed quantitatively to clarify the contribution of Natom to the P/L reaction. We focused on the quantitative relationship between Natom and the produced N-compounds, and found that both N₂ * and N₂⁺ , which are active species other than Natom , contributed to P/L reaction. The production of N-compounds from N₂ * and N₂⁺ was enhanced upon UV irradiation of the water phase, but the production of N-compounds from Natom did not increase by UV irradiation. These results revealed that the P/L reactions starting from Natom and those starting from N₂* and N₂⁺ follow different mechanisms.