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

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 kNO = (3.9 ± 0.3) × 10−11 cm3 s−1 and kNO2 = (3.6 ± 0.3) × 10−11 cm3 s−1 at T = 295 K. The Arrhenius expressions have been determined to be kNO = (9.1 ± 2.7) × 10−12 exp((3.4 ± 0.6) kJ mol−1/RT) cm3 s−1 and kNO2 = (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 τrad(2-C4H9O(Ã)) = (440 ± 80) ns. Quenching rate constants of the 2-C4H9O(Ã) radical were measured to be kq = (4.7 ± 0.3) × 10−10 cm3 s−1 and kq = (5.0 ± 0.4) × 10−12 cm3 s−1 for 2-butylnitrite and nitrogen, respectively.