The reaction between S(1V) and 0 2 in aqueous solution is of importance because of its involvement in flue gas desulfurization processes and in acid rain formation. Despite considerable research, a complete mechanism for the reaction has not been established. In this work a detailed study of the uncatalyzed reaction in the region of pH 4.5 has been carried out. The overall rate law was found to be -d[02]/dt = kobs [HS03-]2[H+]-2[02]o with kobs of 3.6 x lo6 M s-' at 25 "C and ionic strength 0.05 M. The yield of the intermediate S20?-formed duringthe reaction has been determined over the pH range 4.1-6.3. By comparison with the yield of S~0 7~-produced in the reaction of HSO3-with HS05-, it is concluded that S~0 7~-formed in the HS03--02 reaction comes from the reaction between HSO5-and HSO3-, and therefore HSO5-must be an intermediate in the HSO3--O2 reaction in this pH region. From the above yields it is concluded that 60% of the reaction proceeds through the intermediate HS05-. A detailed mechanism consistent with the overall rate law of the reaction has been proposed. A key feature is the proposal that the chain initiation occurs through the reaction of HSO5-with HSO3-to form S O iand Sod-. In order to study the individual rate laws for the initiation, propagation and termination reactions, a relaxation technique was applied. In these experiments, the reaction at a steady state rate was perturbed by suddenly introducing a change in the concentration of HSO3-or H+, and the relaxation of the reaction to the new steady state was recorded. Treatment of these experimental data not only confirmed the HSO3-dependence of the rates of initiation, propagation, and termination in the proposed mechanism but also gave the pH dependence of these reactions. A study of the remarkable inhibitory effect of methanol produced strong support for the proposed initiation reaction. The effect of the introduction of chain initiator S20g2-was also found to be consistent with the mechanism. Relative values of rate constants of reactions in the proposed mechanism have been evaluated from the present experimental data. Evaluation of absolute values of these rate constants requires one additional piece of experimental information, which, depending on the choice, yields a range of values. An arbitrary choice is used to give rough values of the rate constants for initiation, Propagation and termination and typical values for the steady state concentrations of chain carriers independent of the bisulfite concentration.
The oxidation of bisulfite ion by peroxymonosulfate ion, HSOs-, to form sulfate ion has been studied in the pH region 3.8-7.9. The reaction HSOs-+ HS03--* 2S042-+ 2H+ was found to obey the rate law -d[HS05-]/df {fc,aH+ + kbflH*'1 + kc){HSOs-] [HS03 ], where aH+ is the activity of hydrogen ion. At 25 °C and ionic strength 0.0050 M the rate constants fca, kb, and kc have the values 1.27 X 107,6.4X 10-5,and55 M-1 S-1, with the activity of hydrogen ion taken to be dimensionless. For the reaction path corresponding to the ka term, 90% of the reaction yields the intermediate pyrosulfate ion, S2O72-, which then hydrolyzes with about a 1-min lifetime to sulfate and hydrogen ions. Similarly the kc path forms mostly S2O72-as an intermediate. The kb path appears to all go directly to sulfate ion. Possible mechanisms for the various reaction paths are discussed.
We demonstrated transmission of 850-nm dual-mode VCSEL carried NRZ- OOK data at 53 Gbit/s over 100 m graded-index single-mode fiber through heterogeneous mode-field mismatched coupling from lensed MMF with 40% efficiency or 4dB loss.
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