Absolute intensity measurements for the 2·7 μ band of water vapor in a shock tube

Abstract

The apparent spectral absorption coefficients of the H_20 infrared bands in the vicinity of 2·7 µ were measured in a shock tube behind reflected shock waves in an Ar-H_20 mixture. By interrupting an infrared beam at a 60 kc rate and projecting this beam across the shock tube to a monochromator, it was possible to measure simultaneously both emission and absorption of H_20 at 1000°K. The spectral absorption coefficients obtained from emission measurements averaged 9·8 per cent higher than absorption coefficients obtained from absorption measurements, probably due to experimental errors (smaller than usually encountered in shock tube measurements). At 1933°K experimental difficulties precluded simultaneous measurement of infrared emission and absorption, so measurements were restricted to emission. The apparent absorption coefficients were integrated to give the integrated absorption coefficients for the collection of bands near 2·7 µ. Integrated absorption coefficients were 49·8 cm^(-2) atm^(-1), 54·7 cm^(-2) atm^(-1), and 31·6 cm^(-2) atm^(-1) for absorption at 1000°K, emission at 1000°K, and emission at 1933°K, respectively. The two values at 1000°K were in good agreement with those of Goldstein, who made no measurements above this temperature.