Kinetics of Excited Oxygen Formation in Shock-Heated O2-Ar Mixtures.
The formation of electronically excited atomic oxygen was studied behind reflected shock waves using cavity-enhanced absorption spectroscopy. Mixtures of 1% O2-Ar were shock-heated to 5400-7500 K, and two distributed-feedback diode lasers near 777.2 and 844.6 nm were used to measure time-resolved populations of atomic oxygen's5S° and3S° electronic states, respectively. Measurements were compared with simulated population time histories obtained using two different kinetic models that accounted for thermal nonequilibrium effects: (1) a multitemperature model and (2) a reduced collisional-radiative model. The former assumed a Boltzmann distribution of electronic energy, whereas the latter allowed for non-Boltzmann populations by treating the probed electronic states as pseudospecies and accounting for dominant electronic excitation/de-excitation processes. The effects of heavy-particle collisions were investigated and found to play a major role in the kinetics of O atom electronic excitation at the conditions studied. For the first time, rate constants (kM) for O atom electronic excitation from the ground state (3P) due to collisions with argon atoms were directly inferred using the reduced collisional-radiative model, kM(3P →5S°) = 7.8 × 10-17T0.5exp(-1.061 × 105K/T) ± 25% cm3s-1and kM(3P →3S°) = 2.5 × 10-17T0.5exp(-1.105 × 105K/T) ± 25% cm3s-1.
High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering, Stanford University , 452 Escondido Mall, Stanford, California 94305, United States.
Marcel
M
Nations
High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering, Stanford University , 452 Escondido Mall, Stanford, California 94305, United States.
Shengkai
S
Wang
High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering, Stanford University , 452 Escondido Mall, Stanford, California 94305, United States.
Christopher S
CS
Goldenstein
High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering, Stanford University , 452 Escondido Mall, Stanford, California 94305, United States.
David F
DF
Davidson
High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering, Stanford University , 452 Escondido Mall, Stanford, California 94305, United States.
Ronald K
RK
Hanson