We present photodetachment spectra of monohydrogenated gold clusters, and investigate the origin of the vertical detachment energies (VDEs) using calculations based on density functional theory. We show that the standard interpretation that associates VDEs to ground-state isomers is not valid. We propose a new one that is consistent with both the most probable formation route and the structure of the parent clusters, and which gives excellent agreement with experiment. We discuss the implications our results have for the interpretation of VDEs when applied to the study of chemisorption in general. (C) 2002 Elsevier Science B.V. All rights reserved.