Fluorescence excitation spectra of tert-pentoxy [CH3CH2C(O .)(CH3)(2)] and 3-pentoxy radicals were observed fur the first time. The radicals were produced by laser photolysis of the corresponding pentyl nitrites at 355 nm and studied in the wavelength range 345-400 nm. For tert-pentoxy, 12 vibronic bands were labeled in three progressions. One dominant progression corresponds to the C-O stretch mode with initial vibrational interval 551 +/- 10 cm(-1). Two other unknown mode progressions have vibrational intervals of 587 +/- 10 and 631 +/- 10 cm(-1). The transition origin was tentatively assigned at 25 491 +/- 10 cm(-1) (392.3 +/- 0.1 nm). For 3-pentoxy, 15 vibronic bands were labeled in three progressions. The vibrational intervals in each progression are of consistent anharmonic tendency. On the basis of our assignments of the C-O stretch progression, the transition origin T-0, the C-O stretching vibration frequency nu (C-O), and the anharmonic constant chi (C-O) are derived to be 26 437 +/- 10, 578 +/- 6, and -17 +/- 2 cm(-1), respectively. The initial vibrational intervals of two other unknown modes are 596 +/- 10 and 590 +/-10 cm(-1). The fluorescence lifetime of 3-pentoxy was determined to be about 150 ns. The short extent of the laser-induced fluorescence (LIF) excitation spectra of many C-2-C-5 alkoxy radicals is tentatively explained as arising from the opening of a predissociation channel at relatively low excitation energies. Results of efforts to obtain LIF excitation spectra for 10 additional large alkoxy radicals are reported.