State-Specific Modeling of Vibrational Relaxation and Nitric Oxide Formation in Shock-Heated Air

A vibration-specific approach is employed to describe vibrational relaxation and reactive processes in shock-heated air. Models are implemented that include results from recent theoretical calculations for the relevant rate coefficients. Two sets of rate coefficients for the Zeldovich reactions of nitric oxide formation, derived from quasi-classical trajectory calculations, are compared. The relaxation kinetics, nitric oxide formation, and vibrational nonequilibrium behind the shock are discussed in detail. Results show that the nitric oxide formation kinetics is sensitive to the details of the adopted rate coefficients. The effect of the adopted kinetic descriptions (multitemperature, state-to-state) on the postshock plasma radiative signature is investigated. The predicted radiative contribution from the oxygen Schumann-Runge band is dominant in the spectral range 200-300 nm for shock speeds of 5-8 km/s. Comparison to shock-tube absolute intensity measurements has provided indications for improvement of nonequilibrium flow modeling. It is suggested that a kinetic treatment of the radiating electronic states may improve the agreement.