Direct studies on the decomposition of the tert-butoxy radical and its reaction with NO

摘要

The first laser induced fluorescence (LIF) spectrum for the tert-butoxy radical is reported following radical generation by excimer laser photolysis of tert-butyl nitrite. The laser flash photolysis-LIF technique is used to measure the temperature dependence of the rate coefficient for the reaction with NO (T = 200-390 K): (CH_3)_3CO + NO -> (CH_3)_3CONO which can be represented in either Arrhenius or AT~(-n) format: k_3 = (7.8 +- 1.8) * 10~(-12) exp(2850 +- 290 J mol~(-1)/RT) cm~3 molecule~(-1) s~(-1) k_3 = (4.17 +- 0.12) * 10~(-11)(T/200)~(-1.27+-0.07) cm~3 molecule~(-1) s~(-1) and the tert-butoxy decomposition. (CH_3)_3CO -> CH_3COCH_3 + CH_3 Whilst the former reaction shows no pressure dependence (p = 70-500 Torr of helium), the latter reaction is in the fall-off regime over the entire range of experimental conditions (T = 303-393 K, p = 13-600 Torr helium). The fall-off data were fitted using an inverse Laplace transformation/master equation model to give the following Arrhenius parameters: k_2~infinity(T) = (1.4 +- 0.6) * 10~(13) exp[-(57 +- 2) kJ mol~(-1)/RT] These Arrhenius parameters are significantly lower than previous indirect measurements or calculations and the atmospheric and mechanistic implications are discussed. Finally, reaction (3) was also studied by monitoring the temporal dependence of the NO LIF signal following the photolysis of tert-butylnitrite with no additional NO. The results are in good agreement with the tert-butoxy monitoring and allow for an estimation of the rate parameters for the tert-butoxy self reaction.