Atoms, recombination, some rate constants

In the catalytic mechanism, the two consecutive reactions are likely to have radically different rate constants. If the reaction for the proton discharge is relatively small compared with that for the catalytic desorption, the former reaction will determine the rate of the overall reaction in steady state. The catalytic reaction will react quickly when there are adsorbed H atoms to deal with. Since the recombination reaction is assumed here to have a relatively high rate constant (k2), then as soon as some H atoms arrive on the surface, they will form adsorbed H, which will recombine to H2. After gathering a few H2 s together, these will nucleate to form a tiny bubble, which will grow and detach itself from the electrode surface. Because the recombination rate constant is large, the adsorbed H is quickly removed, and 0H remains small. 

Some reactions of ground-state fluorine (2P) atoms generated by 2.45 GHz discharge of dilute F2 + He mixtures have been studied mass spectrometrically with a beam inlet system from a fast flow reactor.3 Fluorine atom concentrations were measured accurately from the consumption of Cl2 in the simple and extremely rapid bimolecular F + Cl2 — FC1 + Cl reaction, for which AL/298 = —9 kJ mol-1, rate constant = 1.1 x 10-10cm3 molecule-1 s-1 at 300 K. The recombination rate of fluorine atoms has been determined at 295 K and at pressures of 10—81Torr, with Ar as carrier gas.4 The data are consistent with a third-order homogeneous reaction whose rate constant is significantly lower than that predicted theoretically and also lower than that for most other atom-recombination reactions under similar conditions. 

The rate constant for this reaction has been measured although there are divergences between the values obtained, it seems likely that the lower value of 1 x 10 cm moH s is correct. Another reaction is the decomposition of ozone, forming groimd state 0( P) atoms, which accounts for some anomalous features of the kinetics of oxygen atom recombination in the products of a discharge in O2... 

Table 5, Rate constants for some atomic radiative recombination processes...

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