Fluorescence excitation spectrum of the 2-butoxyl radical and kinetics of its reactions with NO and NO2

Abstract

The (Ã←) fluorescence excitation spectrum of the 2-C₄H₉O() (2-butoxyl) radical in the wavelength range 345–390 nm was obtained using a combined laser photolysis/laser-induced fluorescence (LIF) technique following the generation of the radicals by excimer laser photolysis of 2-butylnitrite at λ = 351 nm. The fluorescence excitation spectrum shows 5 vibronic bands, where the dominant progression corresponds to the CO-stretching vibration in the first electronically excited state with _CO^′ = (560 ± 10) cm⁻¹. The transition origin was assigned at ₀₀ = (26768 ± 10) cm⁻¹ (λ₀₀ = (373.58 ± 0.15) nm). The kinetics of the reactions of the 2-butoxyl radical with NO and NO₂ at temperatures between T = 223–305 K and pressures between p = 6.5–104 mbar have been determined. The rate coefficients for both reactions were found to be independent of total pressure with k_NO = (3.9 ± 0.3) × 10⁻¹¹ cm³ s⁻¹ and k_NO2 = (3.6 ± 0.3) × 10⁻¹¹ cm³ s⁻¹ at T = 295 K. The Arrhenius expressions have been determined to be k_NO = (9.1 ± 2.7) × 10⁻¹² exp((3.4 ± 0.6) kJ mol⁻¹/RT) cm³ s⁻¹ and k_NO2 = (8.6 ± 3.3) × 10⁻¹² exp((3.3 ± 0.8) kJ mol⁻¹/RT) cm³ s⁻¹. In addition, the radiative lifetime of the 2-C₄H₉O(Ã) radical after excitation at λ = 365.938 nm in the (0,1) band has been determined to be τ^rad(2-C₄H₉O(Ã)) = (440 ± 80) ns. Quenching rate constants of the 2-C₄H₉O(Ã) radical were measured to be k_q = (4.7 ± 0.3) × 10⁻¹⁰ cm³ s⁻¹ and k_q = (5.0 ± 0.4) × 10⁻¹² cm³ s⁻¹ for 2-butylnitrite and nitrogen, respectively.