Lene Krogh Christensen

First direct kinetic study of isotopic enrichment of ozone

The formation kinetics of ozone has been studied using isotopes and pulse radiolysis combined with time-resolved UV absorption spectroscopy. An enhancement of (9.8±2.6)% was found for the rate constant for the reaction of 18O with 18O18O relative to that for the 16O+ 16O16O reaction. The average formation rate for unsymmetric 18O16O16O and 16O18O18O from O2 and 18O18O respectively was enhanced by (14.7±2.8)%. For the formation of a mixture of symmetric and unsymmetric ozone species from O18O the enhancement was (3.6±2.4)%. This leads to the conclusion that both mass and symmetry affect the rate constant for formation of isotopic ozone. The results are compared with recent enhancement studies from the literature, and an apparent conflict is discussed.

Atmospheric chemistry of acetone: Kinetic study of the CH3C(O)CH2O2+NO/NO2 reactions and decomposition of CH3C(O)CH2O2NO2

Pulse radiolysis was used to study the kinetics of the reactions of CH3C(O)CH2O2 radicals with NO and NO2 at 295 K. By monitoring the rate of formation and decay of NO2 using its absorption at 400 and 450 nm the rate constants k(CH3C(O)CH2O2+NO)=(8±2)×10−12 and k(CH3C(O)CH2O2+NO2)=(6.4±0.6)×10−12 cm3 molecule−1 s−1 were determined. Long path length Fourier transform infrared spectrometers were used to investigate the IR spectrum and thermal stability of the peroxynitrate, CH3C(O)CH2O2NO2. A value of k−6≈3 s−1 was determined for the rate of thermal decomposition of CH3C(O)CH2O2NO2 in 700 torr total pressure of O2 diluent at 295 K. When combined with lower temperature studies (250–275 K) a decomposition rate of k−6=1.9×1016 exp (−10830/T) s−1 is determined. Density functional theory was used to calculate the IR spectrum of CH3C(O)CH2O2NO2. Finally, the rate constants for reactions of the CH3C(O)CH2 radical with NO and NO2 were determined to be k(CH3C(O)CH2+NO)=(2.6±0.3)×10−11 and k(CH3C(O)CH2+NO2)=(1.6±0.4)×10−11 cm3 molecule−1 s−1. The results are discussed in the context of the atmospheric chemistry of acetone and the long range atmospheric transport of NOx.