Rate constants for the decomposition of 2-butoxy radicals and their reaction with NO and O2

Abstract

The reactivity of 2-butoxy radicals has been investigated using the laser photolysis/laser induced fluorescence technique. Three reactions have been studied: (i) The rate constants for the reaction with NO have been measured by the same technique at total pressures between 0.03 o p o 0.4 bar of helium and at five temperatures between 295-348 K. No pressure dependence has been found within the experimental error, and a small negative temperature dependence has been found, in agreement with earlier studies: k 1 ¼ (4.4 AE 0.6) Â 10 À12 exp((4.9 AE 0.3) kJ mol À1 /RT) cm 3 s À1 . (ii) The rate constant with O 2 has been measured at room temperature and 0.131 bar of helium: k 2 ¼ (9 AE 2) Â 10 À15 cm 3 s À1 . Significant quenching of 2-butoxy fluorescence by O 2 prevented experiments in a larger temperature range: k q,O 2 ¼ (4 AE 1) Â 10 À11 cm 3 s À1 . (iii) The temperature and pressure dependence of the unimolecular decomposition at total pressures between 0.01 o p o 0.8 bar of helium and at four temperatures between 291-348 K. The low and the high pressure limiting rate constants as well as the broadening factor F cent have been extracted from a falloff analysis of the experimental results: k 3,0,He ¼ 3.2 Â 10 À8 exp(À35.9 kJ mol À1 /RT) cm 3 s À1 , k 3,N ¼ 1.1 Â 10 14 exp(À53.6 kJ mol À1 /RT) s À1 , and F 3,c ¼ 0.87 À T/870 K. We anticipate an uncertainty of AE30% for these rate constants. These results are in excellent agreement with earlier predictions (C.

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

“…The measurements of Hein et al (1999), Falgayrac et al (2004) and Deng et al (2001) are in reasonable agreement. The preferred value for k(298 K) is the mean of these values.…”

“…The recent comprehensive temperature and pressure dependence study of Falgayrac et al (2004) confirms the earlier indications from measurements of and that decomposition is in the fall-off region below 1 bar. The low and the high pressure limiting rate constants as well as the broadening factor F cent extracted from a falloff analysis of their experimental results can be used to calculate rate constants at other pressures ).…”

Experimental and theoretical investigation of the reaction of RO2 radicals with OH radicals: Dependence of the HO2 yield on the size of the alkyl group

“…It can be seen that the OH radical decays are on the same timescale as the increase of the HO 2 concentration, in line with the assumptions that the observed HO 2 radicals are a direct product of (R1) under low O 2 concentrations. The subsequent reaction of the coproduct of HO 2 , the corresponding alkoxy radicals, with O 2 (R6) is still slow on the timescale of the experiment (few milliseconds; see Figure ) for methoxy, ethoxy, 1‐ and 2‐propoxy and 2‐butoxy ( k 6 ' ≈ 130 s −1 ; see Table ), whereas the 1‐butoxy radical will undergo rapid intramolecular isomerization with theory predicting a rate constant at the high‐pressure limit of around 1 × 10 5 s −1 . At the high O 2 concentration experiments (red dots, [O 2 ] = 8 × 10 17 cm −3 ), k 6 becomes fast enough ( k 6 ' ≈ 8 000 s −1 ; see Table ) to convert RO radicals within 100 μs into aldehyde and HO 2 , only the isomerization of 1‐butoxy radicals will still be faster than its reaction with O 2 .…”

Kinetics of the reaction of OH radicals with CH3OH and CD3OD studied by laser photolysis coupled to high repetition rate laser induced fluorescence

“…We have therefore upgraded the classical LIF set-up, employed in our laboratory for many years [3][4][5], with the new high repetition rate laser. We have used this to measure the rate constants of the reactions of hydroxyl radicals with methanol and its deuterated homologue.…”