Quantitative high temperature absorption spectroscopy of NCO at 305 and 440 nm

Abstract

A spectral survey of NCO absorption near the P 2 + p Q 12 head of the [ A 2 Σ + (00 00)← X 2 Π i (00 10)] band was obtained at 1450°K, 0.6 atm using a remotely located cw ring dye laser source and a shock tube. Mixtures of hydrogen cyanide, oxygen and nitrous oxide diluted in argon were shock heated to provide a reproducible steady-state concentration of NCO, and narrow-line absorption was measured in repeated experiments with the laser set at different wavelengths. The peak absorption was found at 440.479 nm (vac). The experimental spectrum was compared with a theoretical model to yield an average Voigt parameter a ≅ 0.1. Additional experiments, in mixtures of cyanogen, oxygen and nitrous oxide diluted in argon, provided a known plateau level of NCO, which was used to infer an absolute absorption coefficient β(1450°K, 0.60 atm) = 110(-50, +130) cm -1 atm -1 at 440.479 nm. This value of β corresponds to an oscillator strength of 0.0026 for the (00 00←00 10) band. Similar experiments were conducted to monitor the absorption around the R 1 head of the [ B 2 Π i (10 10)← X 2 Π i (00 10)] band of NCO, using a frequency doubled cw ring dye laser. The observed spectrum displayed strong broadening, indicating predissociation of the upper state. At the peak absorption wavelength (304.681 nm, vac), we inferred β(1470°K, 0.63 atm) = 40(-19, +48) cm -1 atm -1 and a ≅ 9. This value of β corresponds to an oscillator strength of 0.0031 for the (10 10←00 10) band.