Vibrational Relaxation of Deuterium by a Quantitative Schlieren Method

Abstract

A quantitative schlieren method is described which uses photomultiplier detection of the deflection of a narrow gas‐laser beam to obtain a close approximation to a point measure of density gradient. This method is very sensitive to rapid density changes (a gradient of 5×10⁻⁵ g/liter·mm can be detected in argon) and laboratory relaxation times as short as 0.2 μsec can be measured in the shock tube. The application of this technique to studies of vibrational relaxation is discussed in detail, and the method is compared with the integrated schlieren of Resler and Scheibe for this application. This technique has been applied to a shock‐tube study of the vibrational relaxation of mixtures of D₂ in Ar with the results, in atmosphere·seconds, P_τ = (2.7±0.3)×10⁻¹⁰ exp[(110.5±1.5)/T^⅓], (1100°—3000°K) for pure D₂, and P_τ = (1.0±0.7) × 10⁻⁹ exp[(118±10)/T^⅓], (1600°—3000°K) for D₂ dilute in Ar. The experimental results are in serious disagreement with both the correlation scheme of Millikan and White and the SSH theory.