Photoexcitation and photoionization of argon ahead of a strong shock wave

A chemical kinetic model describing photochemical reactions that are likely to be important in "cold" argon ahead of a strong shock wave 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, partial trapping of the absorbed resonance radiation, subsequent photoionization of excited atoms, photoionization of ground state argon, and certain recombination and deexcitation processes. Specific consideration is given to shock tube geometry, the occurrence of both nonequilibrium and equilibrium regions of variable lengths behind the pressure discontinuity, and the (experimentally) known shock tube wall reflectivity. Theoretical predictions of electron and excited atom concentrations ahead of the shock wave are presented for typical shock tube operating conditions