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

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 (Delta nu(width)) of 2.39 +/- 0.19 cm(-1) and a collision shift (Delta nu(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 Delta nu(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 Delta nu(shift) through an inverse power-law. Copyright (C) 1996 Elsevier Science Ltd