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 < p < 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: k₁ = (4.4 ± 0.6) × 10⁻¹² exp((4.9 ± 0.3) kJ mol⁻¹/RT) cm³ s⁻¹. (ii) The rate constant with O₂ has been measured at room temperature and 0.131 bar of helium: k₂ = (9 ± 2) × 10⁻¹⁵ cm³ s⁻¹. Significant quenching of 2-butoxy fluorescence by O₂ prevented experiments in a larger temperature range: k_q,O2 = (4 ± 1) × 10⁻¹¹ cm³ s⁻¹. (iii) The temperature and pressure dependence of the unimolecular decomposition at total pressures between 0.01 < p < 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 = 3.2 × 10⁻⁸ exp(−35.9 kJ mol⁻¹/RT) cm³ s⁻¹, k_3,∞ = 1.1 × 10¹⁴ exp(−53.6 kJ mol⁻¹/RT) s⁻¹, and F_3,c = 0.87 − T/870 K. We anticipate an uncertainty of ±30% for these rate constants. These results are in excellent agreement with earlier predictions (C. Fittschen, H. Hippler and B. Viskolcz, Phys. Chem. Chem. Phys., 2000, 2, 1677–1683 (); R. Méreau, M.-T. Rayez, F. Caralp and J.-C. Rayez, Phys. Chem. Chem. Phys., 2000, 2, 3765 ()) .