A study of the photodetachment and dissociative photodetachment (DPD) of the C4H9O– isomers tert-butoxide, (CH3)3CO–, and the α-hydroxy carbanion (CH3)2C(CH2)OH– is reported. Photoelectron–photofragment coincidence spectroscopy was used to study these anions at 387, 537, and 600 nm. Supported by CBS-QB3 ab initio calculations, the product mass and translational energy distributions were found to be consistent with dissociation of either highly excited (CH3)3CO radicals or (CH3)2C(CH2)OH alkylhydroxy radicals. Vibrationally resolved photoelectron spectra of stable radicals at 537 and 600 nm in conjunction with Franck–Condon simulations were used to assign the dominant channel to tert-butoxide ((CH3)3CO–) anions thermalized to a vibrational temperature of 550 K. DPD is assigned to highly vibrationally excited radicals produced by photodetachment of unrelaxed tert-butoxide products formed at an effective source temperature of 1400 K. The higher energy carbanion was found to be a minor channel and was not observed to dissociate. Calculated energetics for photodetachment and DPD of (CH3)3CO– and (CH3)2C(CH2)OH– are discussed and compared with the experimental results.