Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

5 ‘CHEMICAL’ MET H 0 D S 319of HC1 may be estimated from the total amount of chlorine added, and the valuecombined with the intensity measurements to calculate the atomic hydrogen concentration.Although in this case the reaction system is probably affected by therelatively large amounts of chlorine added, the agreement between atomic hydrogenconcentrations measured by the two methods is remarkably good.James and SugdenZJ3 have shown that the radiation emitted from flames containingtraces of alkali metals consists of a continuum as well as the atomic emissionlines. The continuum extends from the red to near ultraviolet; its intensity dependslittle upon the temperature, but may be correlated with the concentrationof the hydroxyl radical in the flame. It is concluded that the origin of the continuumis the radiative processA+OH +AOH+hv (30)where A is an alkali metal. The intensity of the continuum can therefore be usedas a measure of the relative hydroxyl concentration in a flame.Resonance emission from alkali metals itself seems to arise from two sources.Padley and Sugden234 have shown that in addition to thermal excitation of thesodium D lines, the processesH+H+Na + H,+Na*H+OH+Na -+ H20+Na*lead to emission of radiation. At “low” temperatures in flames (e.g. N 1500” K)the bulk of the emission does, in fact, arise from reactions (31) and (32). Padleyand Sugden have determined the rate coefficients for the reactions, and with atypical low temperature flame find k31 N 7x lo9 12.mole-2.sec-1, and k32N 2 x 10” 12.mole-’.sec-’. This quantitative data now makes possible calculationof atomic hydrogen and hydroxyl radical concentrations in the flame.Addition of traces of copper salts to a flame produces radiation from a numberof emitters. Bulewicz and Sugden have shown that both CuHZ3’ and CUOH’~~bands appear, and that the balanced processesCu+H+X + CuH+XCu+OH+X + CuOH+X(33)(34)control the formation of the hydride and hydroxide. Thus determination of theintensities of the CuH and CuOH bands gives yet another measure of relative Hor OH concentrations.Three very fast reactions provide methods for the measurement of atomicoxygen, hydrogen and nitrogen concentrations; the techniques are particularlyReferences pp. 336-342