Laser-based studies of reactions of the nitrate radical in aqueous solution.
A new exptl. technique for temp.-dependent studies of the kinetics of NO3 in aq. soln. was developed. In this technique NO3 is produced by excimer laser photolysis of peroxodisulfate anions at 351 nm in the presence of excess nitrate and detected by time-resolved long-path laser absorption using the 632.8 nm line of a HeNe-laser. For the generation reaction of NO3, viz. SO4- + NO3- -> SO42- + NO3, a rate const. of k1 = (5.0 +- 0.5) * 104 l/mol-s at T = 298 K and zero ionic strength is found. For the reactions NO2 + OH- -> NO3- + OH and NO3 + Cl- -> NO3- + Cl, rate coeffs. of k2 = (8.2 +- 0.9) * 107 and k3 = (1.0 +- 0.2) * 107 l/mol-s were detd. at 298 K. Temp.-dependent expts. were used to derive Arrhenius expressions. The rate const. of the reaction of NO3 with dissolved S(IV) was studied over a range of pH values and temp. For the reactions with SO2(aq) and HSO3-, rate coeffs. of k4 = (2.3 +- 0.5) * 108 and k5 = (1.4 +- 0.1) * 109 l/mol-s, resp., at 298 K were obtained. The corresponding temp. dependences are detd. For the reaction of NO3 with SO32- a rate const. of k6 = (3.0 +- 0.4) * 108 l/mol-s was derived at 278 K.
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