Mass spectrometry of neutrals and positive ions in He/CO2 non-equilibrium atmospheric plasma jet

Neutral species and positive ions are measured by means of mass spectrometry in the effluent of the non-equilibrium atmospheric plasma jet operated in He/0%–1%CO 2 gas mixture. The capacitively coupled plasma source is the predecessor of the known COST reference jet with identical performance and it is operated in a diffuse mode with gas temperature close to the room temperature. Threshold ionisation molecular beam mass spectrometry is used to measure absolute densities of CO, O 2 , O and O 3 species. The CO molecules are generated with densities up to 2 × 10 15 cm −3 at 1 W absorbed power. The O 2 density is ∼6 times lower than the CO density and even lower than the O density at level of 4.5 × 10 14 cm −3 . The O 3 density is negligibly small at 4 × 10 12 cm −3 . The measured O 2 , O 3 and O absolute densities add up to ∼57% of the expected oxygen amount. The high O density could indicate that the vibrational excitation of CO 2 is ineffective in this plasma and gas mixture, because O would otherwise react quickly with vibrationally excited CO 2 (v) to form CO and O 2 , the low energy efficiency is in agreement with the possibly low vibrational excitation. The highest energy efficiency is just 5% with 1% conversion efficiency. Ion mass spectrometry have been used to measure positive and negative ions, where only positive ions have been detected. The ion with highest signal is the O 2 + ion, probably due to its low ionisation energy. CO 2 + , O 3 + , ( CO ) 2 + , but no CO + , and protonated clusters or clusters containing water molecules have been detected as well. Neutrals and positive ions have been measured as a function of CO 2 admixture, applied power and distance to the jet nozzle. The observed trends can be used for validation of plasma-chemistry models.