Effect of oxygen atoms on the vibrational kinetics of CO2 and CO revealed by the use of a large surface area material

The effect of oxygen atoms on the vibrational kinetics of CO2 and CO is studied in a DC glow discharge at reduced pressure by means of in situ FTIR spectroscopy. For this study we used two SiO2-based surface configurations: a smooth Pyrex discharge tube and a large specific surface material. The larger surface area enhances the O atom surface recombination into O-2, the dominant O atom loss mechanism in our discharge conditions. The O atom density is thus reduced down to 5%-10% of the density measured with the smooth Pyrex tube, without changing significantly any other relevant plasma parameter (such as reduced electric field, gas temperature or dissociation fraction). The experimental results show a remarkable increase of the vibrational excitation of both CO2 and CO with the large surface material, i.e. low O atom density, demonstrating that atomic oxygen is a strong quencher of the vibrations of both species. In addition we show that, contrary to what could be expected, the use of large specific surfaces does not necessarily lead to lower vibrational excitation. In our experimental conditions, the possible enhanced de-excitation at the surface is compensated by the removal of oxygen atoms. Therefore these experimental results also demonstrate that large surfaces, catalytic or not, may have a significant impact on the plasma kinetics by affecting the recombination of gas phase species.

Automated summary

The study shows that a larger specific surface area leads to a significant increase in vibrational excitation of CO2 and CO due to low O atom density, indicating that atomic oxygen is a strong quencher of the vibrations of both species. Additionally, the use of large specific surfaces does not necessarily result in lower vibrational excitation as previously expected. The results also demonstrate that large surfaces, catalytic or not, may have a notable impact on plasma kinetics by affecting the recombination of gas phase species.