Atoms recombination efficiency

A similar mechanism was proposed earlier by Adamson for photoreduction of Co(NH3)5Br2 +. 48 An observed 4>red of 1.97 for Co(NH3)5I2+ predicts a quantum efficiency of 0.97 for the primary process [reaction (20)]. The mechanism also predicts that 4>red will depend upon the Co(NH3)5I2+ concentration and inversely upon the intensity of the irradiating light in the case where recombination of I atoms is important. Support for the mechanism of Haim and Taube came from the observation that upon flash photolysis of Co(NH3)5I2 + solutions with 370-mp. light, unusually short-lived transient I atoms were observed.62 This was taken to indicate that paths [reaction (21), for example] other than I atom recombination accounted for loss of I atoms in this system. 

Under reducing conditions hydrogen atoms are the main chain carriers. Data from fuel-rich flames indicate that SO2 is efficient in catalyzing H-atom recombination. The H-atom removal presumably involves the following reaction sequence ... 

Fig. 16. The concentration of atoms at a probe, which is behaving as an end plate, as a function of the length of the side tube and the activity of the end plate. The recombination efficiency (7 ) of the end plate is inversly proportional to 6 [see eqn. (97)]. (Courtesy Dickens et al. [57 ].)...

In contrast to the use of large Sf ratios, where attention is focussed on the wall of the tube, Wood and Wise [62, 63] have used short tubes to determine j for the material simulating the end plate. They investigated the recombination efficiency of several metals for H atoms. In the later study [63], their terminal probe was in the form of a heated spiral filament of the metal under investigation. The decrease in energy necessary to maintain the filament at constant temperature was measured and assumed to be proportional to the atom concentration at the cross-section occupied by the filament. The method is preferable to the use of thermocouple probes, whose change in temperature might affect the atom decay profiles. Wood and Wise attribute differences in their results obtained... 

Values of the recombination efficiencies at 300 K of various oxides and of metals which have been completely oxidised by prolonged exposure to molecular and atomic oxygen, are given in Table 9 first-order kinetics... 

These high collision efficiencies have some interesting consequences for the theory of unimolecular reactions. In particular, they imply that the preferred path for fission reactions involve appreciable storage of internal energy in two rotational modes (5). For pyrolysis reactions, they suggest that atom-atom recombination will usually contribute very little to over-all recombination relative to atom-radical or radical-radical reactions. The reason is that the atom-atom recombination is third order. 

B. M. W. Trapnell Liverpool University, England) The relation between H atom combination efficiency and overpotential may be violated by Co, since Kistiakowsky reports this to be the most efficient metal in recombination yet known, although it is difficult to believe that Co has an overpotential of zero. 

A much higher efficiency of H2O as collision partner is observed in H atom recombination, where kjgg( ifi)lktgg AT) is 20 at room tempera-ture and at flame temperatures of 1000-2000 K. The temperature dependence of recombination rate constants is expressed in Table 1.1 in the form... 

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