Frequency-doubled Ring Dye Laser Research Articles

Measurements of the OH A- X (0,0) 306 nm absorption bandhead at 60 atm and 1735 K

The R-branch bandhead near 306.5 nm (32,630 cm −1) of the OH A- X (0,0) system was measured in absorption at discrete frequencies for the condition 1735 K and 60 atm. Mixtures of dilute H 2 O 2 in argon reacted in the reflected-shock region of a high-pressure, high-purity shock tube to form transient concentrations of OH. Absorption was measured using the narrow-linewidth laser light provided by a frequency-doubled ring dye laser. Absolute concentrations of OH were derived through a detailed kinetics model and applied to the measured absorption to extract the absorption coefficient. A fit of the measured, composite absorption spectrum to one synthesized from Voigt profiles of known line strength and line position yielded, for the title conditions, a collision width ( Δν width) of 2.39 ± 0.19 cm −1 and a collision shift ( Δν shift) of −0.83 ± 0.11 cm −1. Though obtained at a density nearly 10 times STP, the measured collision width was found to be consistent with the simple proportionality between Δν width and pressure set by binary collision theory. The measured collision shift, together with other published data, was used to establish the temperature dependence of Δν shift through an inverse power-law.

Shock-tube study of pressure broadening of the A2∑ + - X2Π (0,0) band of OH by Ar and N 2

A rapid-tuning, frequency-doubled ring dye laser was used to make fully-resolved lineshape measurements of OH generated behind reflected shock waves in H 2-O 2-Ar and H 2-O 2-N 2 mixtures. Values of the collisional linewidth were deduced by fitting the observed lineshapes to Voigt profiles. Lines corresponding to transitions with lower-state rotational quantum numbers ranging from 1.5 to 17.5 in the A 2∑ + - X 2Π (0,0) band near 307 nm were probed in order to evaluate a possible J″-dependence in the observed broadening. The temperature range investigated was 1400–4100 K. The collisional broadening parameter, 2γ, was measured at fixed temperature and did not exhibit a strong dependence on the rotational quantum number for either Ar or N 2. The temperature dependence of 2γ for specific J″-values was measured and fit to a power law with an average value of the temperature exponent of 0.8 for both species.