Infrared emission spectra of ammonia-oxygen and hydrazine flames

Abstract

Abstract The infrared emission spectra of a hydrazine decomposition flame and of an ammonia-oxygen diffusion flame have been studied with high-resolution grating spectrometers in the spectral range 600–4000 cm−1. Emission spectra of the hydrazine flame were recorded at various heights in the flame and at two burning pressures. High-resolution absorption spectra of ammonia and hydrazine vapor have been recorded on the same scale for comparison. Emission spectra have also been recorded from two areas of the ammonia-oxygen diffusion flame, one in the ammonia-rich part of the flame and the other in the region of intense yellow radiation due to the NH2 radical. An oxy-hydrogen diffusion flame was examined to establish the spectrum emitted by hot water vapor and by the OH radical. The high-resolution absorption spectrum of ammonia was again recorded on the same scale. There are many emission lines from the hydrazine decomposition flame which can be assigned neither to ammonia nor to hydrazine. These lines are pointed out and discussed, but no definite assignment seems possible from the data because of the large number of short-lived species that might exist in this flame, all containing only nitrogen and hydrogen, and hence all having their infrared bands in similar spectral regions. Nearly all of the emission lines from the ammonia-oxygen flame have been assigned to water, ammonia or the OH radical. Several lines of uncertain assignment appear near 1100 cm−1. These may be due to ammonia, but no correlation exists between them and the ammonia absorption spectrum such as is found in other regions. The most striking new lines are found in the region 2700–3050 cm−1, where a series of twenty-three almost evenly spaced lines occur which cannot be assigned to known lines of water, ammonia or OH. The new lines have tentatively been ascribed to the NH2 radical. In the emission of both flames, the R-branch of the band due to the inversion vibration at 950 cm−1 in ammonia is easily visible, but the P-braneh is not. This phenomenon is attributed to an effect, previously observed in diatomic molecules, which increases the intensity of either the P-branch or the R-branch of a band at the expense of the other branch.