Laser-Induced Fluorescence Excitation Spectra of tert-Butoxy and 2-Butoxy Radicals

Laser-induced fluorescence (LIF) excitation spectra of t -C 4 H 9 O ( tert -butoxy) and 2-C 4 H 9 O (2-butoxy) radicals were investigated in the wavelength range 335−400 nm. The radicals were formed by laser photolysis of the corresponding butyl nitrites at 355 nm. For tert -butoxy, 16 vibronic bands in two progressions were labeled. The dominant progression corresponds to C−O stretching mode with ν‘ C-O = 521 ± 10 cm -1 . The transition origin was tentatively assigned at 25 866 cm -1 (386.6 nm). Numerous bands remain unassigned. The LIF excitation spectrum of 2-butoxy, consisting of 15 vibronic bands in four progressions, was observed for the first time. A C−O stretching frequency ν‘ C - O = 567 ± 10 cm -1 was obtained from the dominant progression. The transition origin was tentatively assigned at 26 185 cm -1 (381.9 nm). Three other progressions are evident, which have different vibrational band intervals: 617 ± 10, 590 ± 10, and 552 ± 10 cm -1 . Zero-pressure fluorescence lifetimes for numerous vibronic bands of tert -butoxy and 2-butoxy were determined to be about 150 and 85 ns, respectively. These spectra can be used as a convenient spectroscopic tool for kinetic studies of butoxy radicals and should provide a starting point for investigations of their excited states structure and dynamics.