Comparison of Thomson scattering measurements and kinetic modeling of electron recombination in nanosecond pulsed discharges with CO$_{\mathrm{2}}$ and O$_{\mathrm{2}}$ diluted in Ar.*

Accurate prediction of electron recombination rates in complex gas mixtures critically influences the development and operational conditions of repetitively pulsed and continuous running low temperature plasma sources. Time and space-resolved recombination in Ar with additions of CO$_{\mathrm{2}}$ and O$_{\mathrm{2}}$ is studied through combined experimental measurements by Thomson scattering and kinetic modeling. Single nanosecond pulsed discharges are produced in a pin-to-sphere discharge geometry at a pressure of 80 Torr. Subsequent to pulsed excitation at 20 kV, spatiotemporal Thomson scattering measurements of electron density and electron temperature are obtained. Relative to a pure argon discharge, addition of 0.75{\%} CO$_{\mathrm{2}}$ suppresses the initial plasma density by nearly a factor of two, while O$_{\mathrm{2}}$ dilution of 1.0{\%} slightly decreases both the initial electron density and electron temperature. These results are compared to a kinetic model of the discharge afterglow developed to study recombination processes and plasma chemistry. The model results clarify that the presence of molecular ions accelerates the plasma decay through dissociative recombination and the molecular gas admixture accelerates the relaxation of the electron temperature at low electron energies, especially in the case of CO$_{\mathrm{2}}$ addition.