REACTIVITY TRENDS IN REACTIONS OF THE NITRATE RADICAL (NO3) WITH INORGANIC AND ORGANIC CLOUDWATER CONSTITUENTS

In an extended study on the reactivity ofthe nitrate radical in aqueou s solution, NO3 radicals were produced by excimer laser photolysis of peroxodisulfate anions in the presence of excess nitrate. For the time -resolved detection of NO3, a sensitive laser long path absorption tec hnique at 632.8 nm was applied. For the reaction of NO3 with H2O2 (rea ction 1) the temperature dependent rate coefficient was found to be k( 1)(T) = (4.0 +/- 0.5).10(9) exp[-(2000 +/- 850)/T] L mol(-1) s(-1), co rresponding to k(1) = (7.0 +/- 1.2) 10(6) L mol(-1) s(-1) at 298 K. Th e rate coefficients of the reactions of NO3 with acetone (reaction 2), tetrahydrofuran (reaction 3), and hydrated formaldehyde (reaction 4) were determined at T = 298 K to be k(2) = (4.4 +/- 0.6).10(3) L mol(-1 ) s(-1), k(3) = (2.1 + 0.1).10(7) L mol(-1) s(-1), and k(4) = (7.8 +/- 1.2).10(5) L mol(-1) s(-1), respectively. For the reactions of NO3 wi th the alcohols methanol (reaction 5), ethanol (reaction 6), 1-propano l (reaction 7), 2-propanol (reaction 8), and 2-methyl-2-propanol (reac tion 9) the following rate constants at T = 298 K were obtained: k(5) = (5.1 +/- 0.3) 10(5) L mol(-1) s(-1), k(6) = (2.4 +/- 0.5).10(6) L mo l(-1) s(-1), k(7) = (3.2 +/- 0.1) 10(6) L mol(-1) s(-1), k(8) = (3.7 /- 0.9).106 L mol(-1) s(-1), and k(9) = (6.6 +/- 0.7).10(4) L mol(-1) s(-1), respectively. A linear relationship between the logarithm of th e rate coefficients and C-H bond dissociation energies was found, whic h is described by the expression Ig (k(NO3)(H)) = (44 +/- 8) - (0.1 +/ - 0.02).D-C-H/kJ mol(-1). A comparison of aqueous phase and correspond ing gas phase rate constants of NO3 provides a linear correlation, whi ch is expressed by Ig (k(NO3(g)+X))= (0.58 +/- 0.15) + (0.79 +/- 0.2). lg (k(NO3(nq)+X)).