Oxygen Vibrational Relaxation Times: Shock Tube/Laser Absorption Measurements

Abstract

The vibrational relaxation times of oxygen were measured using laser absorption spectroscopy behind incident and reflected shocks in a shock tube. The Bethe–Teller equation was used to model the vibrational relaxation, which (along with the shock jump relations) was used to model the gas dynamics conditions throughout the nonequilibrium relaxation process. The absorbance was modeled based on these gas dynamics conditions while adjusting the vibrational relaxation time to fit the model to the measured oxygen absorbance time history at wavelengths 210–230 nm in the Schumann–Runge system. Undiluted oxygen was studied behind incident shocks at initial postshock translational/rotational temperatures from 1000 to 3300 K and pressures from 0.05 to 0.7 atm, while a mixture of 2% oxygen in argon was studied behind incident and reflected shocks at initial translational/rotational temperatures from 1000 to 4000 K and pressures from 0.2 to 1 atm. Good agreement was found with prior experimental work by White and Millikan, Losev and Generalov, and Camac; however, the current relaxation time data have less scatter and reduced uncertainty. The current results are also in excellent agreement with the well-known relaxation time recommendations of Millikan and White.