Determination of local concentration of H2O molecules and gas temperature in the process of hydrogen – oxygen gas mixture heating by means of linear and nonlinear laser spectroscopy

Abstract

Employing the methods of linear absorption spectroscopy and nonlinear four-wave mixing spectroscopy using laserinduced gratings we have simultaneously measured the local concentrationsof H2O molecules and the gas temperature in the process of the H2 – O2 mixture heating. During the measurements of the deactivation rates of pulsed-laser excited singlet oxygen O2 (b 1Σ+g) in collisions with H2 in the range 294 – 850 K, the joint use of the two methods made it possible to determine the degree of hydrogen oxidation at a given temperature. As the mixture is heated, H2O molecules are formed by 'dark' reactions of H2 with O2 in the ground state. The experiments have shown that the measurements of tunable diode laser radiation absorption along an optical path through the inhomogeneously heated gas mixture in a cell allows high-accuracy determination of the local H2O concentration in the O2 laser excitation volume, if the gas temperature in this volume is known. When studying the collisional deactivation of O2 (b 1Σ+g) molecules, the necessary measurements of the local temperature can be implemented using laser-induced gratings, arising due to spatially periodic excitation of O2 (X3Σ-g) molecules to the b 1Σ+g state by radiation of the pump laser of the four-wave mixing spectrometer.