The kinetics of the rapid reaction between Cr(aq)OO(2+) and NO were determined by laser flash photolysis of Cr(aq)NO(2+) in O(2)-saturated acidic aqueous solutions, k = 7 x 10(8) M(-1) s(-1) at 25 degrees C. The reaction produces an intermediate, believed to be NO(2), which was scavenged with ([14]aneN(4))Ni(2+). With limiting NO, the Cr(aq)OO(2+)/NO reaction has a 1:1 stoichiometry and produces both free NO(3)(-) and a chromium nitrato complex, Cr(aq)ONO(2)(2+). In the presence of excess NO, the stoichiometry changes to [NO]/[Cr(aq)OO(2+)] = 3:1, and the reaction produces close to 3 mol of nitrite/mol of Cr(aq)OO(2+). An intermediate, identified as a nitritochromium(III) ion, Cr(aq)ONO(2+), is a precursor to a portion of free NO(2)(-). In the proposed mechanism, the initially produced peroxynitrito complex, Cr(aq)OONO(2+), undergoes O-O bond homolysis followed by some known and some novel chemistry of Cr(aq)O(2+) and NO(2). The reaction between Cr(aq)O(2+) and NO generates Cr(aq)ONO(2+), k > 10(4) M(-1) s(-1). Cr(aq)OO(2+) reacts with NO(2) with k = 2.3 x 10(8) M(-1) s(-1).

The carbonate ion inhibited aqueous decomposition of ozone was studied by the stopped-flow method at 25.0 ± 0.1 °C in 0.5 M NaClO4. It was shown that the rate of decomposition sharply decreases and reaches a limiting value by increasing the carbonate ion concentration. A detailed kinetic model was developed for the interpretation of the results. The corresponding set of rate constants was calculated by simultaneously fitting kinetic traces obtained at the absorption maxima of O3 (260 nm), O3 - (430 nm), and CO3 - (600 nm). It was confirmed that the inhibition is mainly due to the removal of two dominant chain carrier radicals, OH and O3 -, via the following reaction steps:  CO3 2- + OH → CO3 - + OH-, k = (1.0 ± 0.1) × 108 M-1 s-1, and CO3 - + O3 - → CO3 2- + O3, k = (5.5 ± 0.5) × 107 M-1 s-1. The kinetically less significant reactions of other transient species are also discussed in detail. The mechanism gives proper description of ozone decay, the formation and subsequent disappearance of ozonide ion and carbonate ion radicals, as well as the concentration change of other intermediates over the pH range 10.7−12.8. The model predicts that ozone decomposition occurs in a simple first-order process at high CO3 2- concentration, in agreement with the experimental data.

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In aqueous solutions, the aquachromyl(IV) ion, Cr(aq)O(2+), disproportionates to Cr(aq)(3+) and HCrO(4)(-). The reaction exhibits second-order kinetics with an inverse [H(+)] dependence, -d[Cr(aq)O(2+)]/dt = 38.8[Cr(aq)O(2+)](2)[H(+)](-1) at 25 degrees C. The combination of the rate law and substantial kinetic isotope effect, k(H)/k(D) = 6.9, suggests a mechanism whereby a hydrogen atom is abstracted from a coordinated molecule of water or hydroxo group within a singly deprotonated transition state. The buildup of chromate is more complicated and somewhat slower than the loss of chromyl, suggesting the involvement of intermediates.