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

The fluorescence excitation spectrum of the tert-C4H9O((X) over tilde) (ter t-butoxy) radical in the wavelength range 330-440 nm was obtained using a c ombined laser photolysis/laser-induced fluorescence (LIF) technique. The ra dicals were generated by excimer laser photolysis of di-tert-butylperoxide at lambda = 248 nm. Its fluorescence excitation spectrum shows 16 vibronic bands in two progressions, where the dominant progression corresponds to th e CO stretching vibration in the first electronically excited state with <( nu)over tilde>(CO)' = (515 +/- 10) cm(-1). The transition origin was assign ed at <(nu)over tilde>(00) = (25 836 +/- 10) cm(-1) [lambda(00) = (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 f ound to be independent of total pressure with k(NO) = (2.9 +/- 0.2) x 10(-1 1) cm(3) s(-1) (5-80 Torr) and k(NO2) = (2.50 +/- 0.2) x 10(-11) cm(3) 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) x 1 0(-12) exp[(3.2 +/- 0.8) kJ mol(-1)/RT] cm(3) s(-1) and k(NO2) = (3.5 +/- 1 .2) x 10(-12) exp[(4.6 +/- 0.7) kJ mol(-1)/RT] cm(3) s(-1). Additionally, t he radiative lifetime of the tert-C4H9O((A) over tilde) radical after excit ation at lambda = 341.576 nm was determined to be tau(rad)[tert-C4H9O((A) o ver tilde)] greater than or equal to (1.5 +/- 0.1) mu s. The fluorescence s pectrum of electronically excited tert-butoxy radicals in the range lambda = 375-575 nm was obtained following the photolysis of tert-butylnitrite at 193 nm.