Chemiluminescence relative rate analysis

Relative Rate Constants. A variety of new techniques have been developed for obtaining accurate measurements of relative rate constants for hydrogen abstraction reactions by atomic fluorine (t.i6.18.19.22.2i -27. 5-8q.87.88). Of principal present interest ai4 the HF chemiluminescence (81 85). H F product analysis (2 -26). and Indirect atom loss (87.88) procedures. 

A comparison of 300"K relative rate constants obtained using chemiluminescence and H F product analysis methods is presented in Table VIII. The (ka/ki) values listed in column three have been based upon the revised thermal reaction fraction (cf. Table v), upon new sample data in many instances, upon the modified data reduction procedures described above, and upon the Arrhenius parameters listed in Table XII. These updated results are intended to supplant the F-to-HF rate constants reported previously from this laboratory (25). 

A kinetic analysis of the results, based on (17) and its O+OH analog, is in satisfactory agreement with observations on a wide variety of flames. These flames are relatively cool, and the concentrations of H and OH exceed their equilibrium values even in the burned gases, so that the observed sodium emission is definitely chemiluminescent. The third order rate coefficients for excitation by H+H and H+OH are estimated to be 8 x 109 and 2x 1010 l2.mole-2.sec-1, corresponding to an efficiency near unity per triple collision. The possible importance of mechanisms of the type (14,15) has not been carefully studied. 

Sample Chemiluminescence Analysis Induction time Oxidation rate (relative units)(relative units) Oven life (days)... 

In order to optimise the manifold design of the flow system, the lifetimes of the excited states of the molecules should be considered, because the processed sample is in motion. In the situation of too high a flow rate and too small a flow cell, a fraction of the excited molecules could exit the flow cell without emitting light. On the other hand, if the flow rate is too low, a significant fraction of the molecules may emit radiation before reaching the flow cell. Both situations can lead to a decrease in the analytical sensitivity. This feature can be considered as a "time window" in flow analysis and the effect is more pronounced in phosphorimetric methods where light emission is slow relative to fluorimetric methods [65]. This is also true for chemiluminescence and bioluminescence, as discussed in the next section. 

The modification of the infrared spectrum as the F atom spray is turned on and off is observed. This chemiluminescence depletion (CD) method yields relative reaction rates of several vibrational levels, and it can provide state-to-state data if the molecular product of the second reaction is itself an infrared emitter. Moreover, some information can be obtained about the dependence of reaction rate on reagent rotation. The main difficulty is that the CD spectrum really depends on a complex matrix of detailed rate constants—for inelastic as well as reactive processes—with the result that the analysis is not straightforward. 

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