Shock-tube measurements of coupled vibration–dissociation time-histories and rate parameters in oxygen and argon mixtures from 5000 K to 10 000 K

Abstract

Shock-tube experiments were conducted behind reflected shocks using ultraviolet (UV) laser absorption to measure coupled vibration–dissociation (CVDV) time-histories and rate parameters in dilute mixtures of oxygen (O2) and argon (Ar). Experiments probed 2% and 5% O2 in Ar mixtures for initial post-reflected-shock conditions from 5000 K to 10 000 K and 0.04 atm to 0.45 atm. A tunable, pulsed UV laser absorption diagnostic measured absorbance time-histories from the fourth, fifth, and sixth vibrational levels of the electronic ground state of O2, and experiments were repeated—with closely matched temperature and pressure conditions—to probe absorbance time-histories corresponding to each vibrational level. The absorbance ratio from two vibrational levels, interpreted via an experimentally validated spectroscopic model, determined vibrational temperature time-histories. In contrast, the absorbance involving a single vibrational level determined vibrational-state-specific number density time-histories. These temperature and state-specific number density time-histories agree reasonably well with state-to-state modeling at low temperatures but deviate significantly at high temperatures. Further analysis of the vibrational temperature and number density time-histories isolated coupling parameters from the Marrone and Treanor CVDV model, including vibrational relaxation time (τ), average vibrational energy loss (ε), vibrational coupling factor (Z), and dissociation rate constant (kd). The results for τ and kd are consistent with previous results, exhibit low scatter, and—in the case of vibrational relaxation time—extend measurements to higher temperatures than previous experiments. The results for ε and Z overlap some common models, exhibit relatively low scatter, and provide novel experimental data.