Fluorescence excitation spectrum of the tert-butoxy radical and kinetics of its reactions with NO and NO2

Abstract

The fluorescence excitation spectrum of the tert-C₄H₉O() (tert-butoxy) radical in the wavelength range 330–440 nm was obtained using a combined laser photolysis/laser-induced fluorescence (LIF) technique. The radicals were generated by excimer laser photolysis of di-tert-butylperoxide at λ=248 nm. Its fluorescence excitation spectrum shows 16 vibronic bands in two progressions, where the dominant progression corresponds to the CO stretching vibration in the first electronically excited state with _CO^′=(515±10) cm⁻¹. The transition origin was assigned at ₀₀=(25836±10) cm⁻¹ [λ₀₀=(387.06±0.15) nm]. The kinetics of the reactions of the tert-butoxy radical with NO and NO₂ over the temperature range T=223–305 K and pressure range p=5–80 Torr were determined. The rate coefficients for both reactions were found to be independent of total pressure with k_NO=(2.9±0.2)×10⁻¹¹ cm³ s⁻¹ (5–80 Torr) and k_NO2=(2.50±0.2)×10⁻¹¹ cm³ s⁻¹ (5–80 Torr) at T=295 K. The Arrhenius expressions for the reactions of tert-butoxy with NO and NO₂ were determined to be k_NO=(7.6±1.2)×10⁻¹² exp[(3.2±0.8) kJ mol⁻¹/RT] cm³ s⁻¹ and k_NO2=(3.5±1.2)×10⁻¹² exp[(4.6±0.7) kJ mol⁻¹/RT] cm³ s⁻¹. Additionally, the radiative lifetime of the tert-C₄H₉O(Ã) radical after excitation at λ=341.576 nm was determined to be τ^rad[tert-C₄H₉O(Ã)](1.5±0.1) μs. The fluorescence spectrum of electronically excited tert-butoxy radicals in the range λ=375–575 nm was obtained following the photolysis of tert-butylnitrite at 193 nm.