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

A spectral survey of NCO absorption near the P₂ + ^pQ₁₂ head of the A²Σ + (00⁰0)←X²Π_i(00¹0)] 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 (00⁰0←00¹0) band.Similar experiments were conducted to monitor the absorption around the R₁ head of the B²Π_i(10¹0)←X²Π_i(00¹0)] 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 (10¹0←00¹0) band.