THE STABILITIES OF THE GAS-PHASE IONS CO3- AND HCO3-, TOGETHER WITH THE KINETICS OF BOTH THEIR PRODUCTION AND REMOVAL IN O-2-RICH FLAMES OFH-2-2+N-2(O)

Six well-defined laminar flat premixed oxygen-rich flames of H-2 + O-2 + N-2 have been burnt with CO2 added to the burner supplies. In addit ion, trace quantities of an alkali metal (K or Cs) were present and pr ovided free electrons in the hot gases (temperature similar to 2000 K) The positive ions were found to be K+ or Cs+ by continuously sampling a flame into a mass spectrometer. The negatively charged species were mainly OH-, O-2(-), CO3-, HCO3- and the free electron. It is conclude d that HCO3- is formed from OH- in the forward step of OH- + CO2 + M r eversible arrow HCO3- + M, (I) where M is any molecule in the flame ca pable of removing energy from the other two reacting species in the fo rward step. In fact, well downstream in a flame, reaction (I) is equil ibriated and also has a time constant small enough for its equilibrium position to shift, while the sample is cooled on entering the mass sp ectrometer. Techniques were found to quantify these perturbations of a n ion spectrum, which enabled the equilibrium constant of (I) to be de duced as a function of temperature. As a result, values of Delta H- an d Delta S- for reaction (I) were also obtained. That reaction (I) is e quilibrated in these flames and also is perturbed by the process of sa mpling into a vacuum system enables the rate constants for the forward and reverse steps to be quantified. The ion CO3- is at least three ti mes more abundant than HCO3-. The reactions HCO3- + OH reversible arro w CO3- + H2O (X) are responsible for creating and removing CO3-. React ion (X) is also equilibriated well downstream in a flame, but its equi librium position is normally not shifted during sampling. Thus, it pro ved possible to measure its equilibrium constant over a range of tempe ratures, leading to corresponding values of Delta H- and Delta S-. Tha t reaction (X) appears not to be shifted on cooling a flame sample whi le it enters the mass spectrometer, in fact, enables values of the rat e coefficients for the forward and reverse steps of (X) to be deduced. In addition, the stabilities of both CO3- and HCO3- are fully charact erized by this study. The situation early in one of these flames, i.e. in or near the reaction zone, seems to be one where steady-state rela tionships hold, rather than equilibrium being established locally.