Figure 10. A shielding gas of pure oxygen strongly inhibits the presence of OH and N₂ molecules in the gas phase.

The emission spectra of the molecular bands of (A) OH (at around 309 nm), (B) N₂(C) (Second Positive System at around 337 nm) and (C) N₂⁺ (First Negative System at around 391 nm) and the atomic lines of (D) He (at around 706 nm) and (E) O (at around 777 nm) were recorded in the absence (no shielding) or presence (pure O₂ shielding) of a shielding of pure O₂. The gas flow of He was set to 100 sccm and the plasma is created by applying high voltage pulses with amplitude of 5.5 kV.