Recombination Coefficient of Electrons with NO+ Ions in Shock-Heated Air

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Abstract
A measurement of the electron-positive-ion recombination coefficient has been made in air of density near 0.1 atm. and of temperature about 2900°K, yielding the value, α = (4 ± 2) × 10−8 cm3 sec−1. The results indicate that dissociative recombination, NO+ + e− → N + O, is the dominant electron depletion process. Air behind a reflected shock wave at a temperature of 3600°K is expanded rapidly into a thin-wall quartz tube. The tube serves as a post in three X-band waveguides. Electron densities are computed from the measured phase shifts of transmitted microwave signals. The relation between electron density and phase shift is determined with discharge plasmas of known electron densities. The recombination coefficient is computed from the measured electron depletion rate and the time variation of the temperature and velocity of the gas in its unsteady expansion down the quartz tube. The effects of diffusion, attachment, and impurities are also investigated. The measured value of α is in reasonable agreement with that of Lin et al., at 5000°K when a T−3/2 temperature dependence is assumed. This result is also compared with other laboratory measurements near 300°K.

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