Atomic hydrogen concentration

Two thermocouples, Em at x = 0 and Ex at a distance x, permit the monitoring of the atomic hydrogen concentration change along the side-tube. The atoms recombining on the thermocouple tip covered by the active catalyst evolve the heat of reaction and thus the thermoelectric power becomes a relative measure of the concentration of atoms in the gas phase. Finally, one obtains for the direct use in an experimental work the following equation... 

The same reaction mechanism operated on the surfaces of both kinds of catalyst on metals and their hydrides as well. The reaction proceeded according to the Rideal-Eley mechanism and was of first order with respect to the atomic hydrogen concentration in the gas phase. 

The maximum hydrogen concentration cm = 3 corresponds to the formation of OH3 hydrofullerite, i.e., in this case atomic hydrogen concentration in reference to the number of fullerenes cannot exceed x = 3. 

However, Sievert s Law relates atomic hydrogen concentration within the metai to partial pressure by ... 

Oh Xh, with Oh being the expansion coefficient and Xh being the atomic hydrogen concentration in the units mol(H)/mol(Me), it follows that... 

The discussion of emission spectroscopy will be concluded by a description of a rather unusual application. Bay and Steiner have measured atomic hydrogen concentrations in the presence of molecular hydrogen by microwave excitation of the atomic hydrogen line spectrum. With low power fed into the gas (ca. 5 watts), there is not enough energy available for the dissociation of molecular hydrogen and subsequent excitation. Thus the measured intensities of the atomic hydrogen lines correspond to the concentrations of atoms already present in the reaction mixture. The method is curiously similar to that adopted to detect atoms and free radicals by mass spectrometry (see Section 3). 

The kinetics of the reaction have been investigated , and it is therefore possible to determine atomic hydrogen concentrations from the rate at which ortho-H.2 appears in a system initially containing only para-H2. Ortho-para hydrogen ratios may be determined by vapour phase chromatography using charcoal columns , and this technique probably replaces the earlier thermal conductivity measurements (for a description of the latter see ref. 220). The rate coefficients of reaction (23) cannot be fitfed to a simple Arrhenius expression Schulz and LeRoy find that their results can be expressed by... 

The corresponding reaction for sodium is negligible, so that measurement of the intensities of the resonance lines for the two metals may be combined with an estimated equilibrium constant for (28) to give the atomic hydrogen concentration. The method is satisfactory in that only trace amounts of the alkali ihetal salt need be added, and no appreciable perturbation of the reaction system occurs. Values for the atomic hydrogen concentrations obtained by the method described were compared with those calculated when chlorine was added to a flame already containing traces of sodium An equilibrium is again established as a result of the reactions... 

Emission from HNO lies mainly in the near infrared, and may be detected with suitable photomultipUers. Titration by nitrogen dioxide to the end-point (i.c. extinction of chemiluminescence) then gives the atomic hydrogen concentration, dyne and Thrush point out that the stoichiometry implied in equation (36) is only correct in the absence of molecular hydrogen, and that up to three molecules of NO2 may be consumed for every hydrogen atom if much H2 is present they show, however, that at room temperature and with [H]/[H2] > i equation (36)... 

However, to relate CPC to the membrane permeance according to eqn (14.1), it is necessary to choose an appropriate form of the bulk driving force. Concerning this issue, it should be considered that, when the rate-determining step of the overall permeation process is the diffusion in the Pd-based layer and, also, the atomic hydrogen concentration inside membrane... 

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