Determination of Atomic Oxygen in Atmospheric Plasma from Oxygen Isotope Exchange

Oxygen scrambling is observed when a 1:1 mixture of 16 O 2 and 18 O 2 in nitrogen/helium buffer (total O 2 : 5–20%) is treated at atmospheric pressure in a surface discharge plasma reactor. The statistical isotope distribution ( 16 O 2 / 18 O 2 / 16 O 18 O = 1:1:2) is achieved with a very low SIE (i.e., the energy per unit volume). This process, implemented by kinetic simulations, is proposed as a chemical probe for the determination of the average O‐atom density in atmospheric plasmas. It was found that, within the explored composition range (5–20% O 2 in N 2 /He buffer), the average O‐atom density increases with SIE, while it decreases with increasing content of O 2 in the gas being treated. In contrast, an opposite trend is observed for ozone production, which increases with the concentration of O 2 in the treated gas. These observations are consistent with the known reaction of O‐atoms with O 2 to form ozone, which, at constant total pressure, is expected to favor ozone production as the concentration of O 2 is increased.