Precursor photoexcitation and photoionization of argon in shock tubes

TLDR: In this paper, a chemical kinetic model describing photochemical reactions that are likely to be important in "cold" argon ahead of a strong shock wave in a shock tube is examined on a quantitative basis.

Abstract: A chemical kinetic model describing photochemical reactions that are likely to be important in "cold" argon ahead of a strong shock wave in a shock tube is examined on a quantitative basis. The model includes the propagation of resonance radiation far from the shock front in the wings of the resonance absorption line, imprisonment of the absorbed resonance radiation, subsequent photoionization of excited atoms, photoionization of ground state argon, and certain recombination and de-excitation processes. Specific consideration is given to shock tube geometry, the finite extent of the equilibrium region and the (experimentally) known shock tube wall reflectivity. Theoretical predictions of excited atom and argon ion concentrations in the precursor region are presented for typical shock tube operating conditions. The regimes favorable to the production of argon ions by photoionization of ground state argon and by photoionizati on of photoexcited argon, respectively, are delineated.