Determination of local concentration of H{sub 2}O molecules and gas temperature in the process of hydrogen - oxygen gas mixture heating by means of linear and nonlinear laser spectroscopy

Employing the methods of linear absorption spectroscopy and nonlinear four-wave mixing spectroscopy using laserinduced gratings we have simultaneously measured the local concentrations of H{sub 2}O molecules and the gas temperature in the process of the H{sub 2} - O{sub 2} mixture heating. During the measurements of the deactivation rates of pulsed-laser excited singlet oxygen O{sub 2} (b {sup 1}{Sigma}{sup +}{sub g}) in collisions with H{sub 2} 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, H{sub 2}O molecules are formed by 'dark' reactions of H{sub 2} with O{sub 2} 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 H{sub 2}O concentration in the O{sub 2} laser excitation volume, if the gas temperature in this volume is known. When studying the collisional deactivation of O{sub 2} (b {sup 1}{Sigma}{sup +}{sub g}) molecules, the necessary measurements of the local temperature can be implemented using laser-induced gratings, arising due to spatially periodic excitation of O{sub 2} (X{sup 3}{Sigma}{sup -}{sub g}) molecules to the b {sup 1}{Sigma}{sup +}{sub g} state by radiation of the pump laser of the four-wave mixing spectrometer. (laser spectroscopy)