Laser absorption measurements of OH, NH, and NH2 in NH3/O2 flames: Determination of an oscillator strength for NH2

Abstract

We have used laser diagnostics to probe atmospheric pressure ammonia–oxygen flames. Absorption from a tunable dye laser was used to measure concentration profiles of OH, NH, and NH₂ radicals at fuel equivalence ratios φ of 1.28, 1.50, and 1.81. The absolute concentrations of OH and NH and the product of the NH₂ concentration and the NH₂ oscillator strength were derived as a function of height above the flat flame burner. These measurements indicate that the reaction NH₂+OH?NH+H₂O is equilibrated near the flame front, as well as in the post flame region. It was possible to use these measurements to derive an oscillator strength f_i = (2.04±0.44)×10⁻⁴ for the ^PQ_1,7 line in the (0,9,0)←(0,0,0) vibrational band of the A ²A₁←X ²B₁ transition of NH₂. Rotational temperatures of OH were obtained from absorption measurements on a variety of rotational lines. These temperatures suggest the possibility of excess rotational energy in OH in the flame front regions of the φ = 1.28 and φ = 1.50 flames.