Measurement of collision broadening of the P 1(5) line of (0,0) band of OH A 2Σ +←X 2Π transition at high temperatures

Abstract

Even for the well-studied and ubiquitous species, OH, the current state of theoretical development of broadening theory does not allow extrapolation from low-temperature laboratory measurements to the range of practical combustion devices. We performed a series of experiments at typical combustion conditions to determine the collision broadening of the P 1(5) line of the (0,0) band of OH A 2Σ +←X 2Π transition by Ar in shock-heated H 2–O 2–Ar mixtures and by air in H 2–air flames over a wide range of stoichiometry ( φ=0.01–10.0), temperature ( T=780–2440 K), and pressure ( p=0.7–10.0 atm). The values of the collision width, Δν C, were acquired by fitting Voigt profiles to the measured spectral line shapes in flames and to the peak absorption coefficients ( k ν 0) in shock tube experiments. Collision broadening parameters (2 γ Ar, 2 γ N 2 , and 2 γ H 2 O ) were then calculated assuming the linear dependence of Δν C with pressure—the 2 γ N 2 and 2 γ H 2 O values were inferred from 2 γ Air and the equilibrium concentration of N 2 and H 2O of a given flame. The temperature dependences of 2 γ i in our temperature range are, respectively, 1.0, 0.75, and 0.87 for Ar, N 2, and H 2O. The collision broadening cross sections ( σ) deduced from 2 γ i values are expressed with an assumed form, σ i ( T)= σ i , 0( T 0/ T) k , T 0=1000 K: for Ar, σ Ar,0=63.3 (Å 2), k=0.50; for N 2, σ N 2 , 0 = 68.0 (Å 2), k=0.25; for H 2O, σ H 2 O , 0 = 188.8 (Å 2), k=0.37.