Photochemistry of NO3 and the kinetics of the N2O5--O3 system

The kinetics of the nitrogen pentoxide catalyzed decomposition of ozone were studied in the dark and with photolytic light absorbed by the NO3 radical. Ultraviolet, visible, or infrared absorption cross sections were measured for N2O5, HNO3, NO2 and NO3. The equilibrium constant for N2O5 reversible NO2 + NO3 was found to be (molecules cm-3, 298--329 K) K = (8.4 +- 1.8) x 1026 exp[-(11180 +- 100)/T]. The rate constants for several reactions were measured: (cm3 molecule-1s-1) 2NO3 → 2NO2 + O2, g = (8.5 +- 2.8) x 10-13 exp[-(2450 +- 100)/T]; O + N2O5 → product, m less than or equal to 2 x 10-14; O + NO3 → O2 + NO2, n = (1.0 +- 0.4) x 10-11. By combining the equilibrium constant K with literature values of Ke and Kf, rate constants for reactions e and f were evaluated: NO2 + NO3 → NO + O2 + NO2, e = (2.5 +- 0.5) x 10-14 exp[-(1230 +- 100)/T]; NO + NO3 → 2NO2, f = (1.9 +- 0.4) x 10-11 at 297 K. At 1 atm total pressure, the photolysis of NO3 occurs with a primary quantum yield less than one in the red region of the spectrum. The solar photolysis constants at 298 K for the two paths of dissociation are consistent with the following values: NO3 + hν → NO + O2, j1 = 0.040 +- 0.02 s-1; NO3 + hν → NO2 + O, j2 = 0.099 +- 0.02 s-1. The average quantum yield for process two was approximately 0.77 for light with wavelengths between 470 and 610 nm, and that for process one was about 0.23 between 470 and 610 nm but only 0.07 in the strong absorption region between 610 and 670 nm. The photolysis constants may be larger at lower total pressures. Infrared absorption ascribed to NO3 is due to N2O5; previously reported visible cross sections for NO3 were found to be about a factor of 4 too low and are corrected here; previously reported ultraviolet cross sections for N2O5 are reversed slightly