The equilibrium structures and vibrational frequencies of the radical, monomer and dimer of alpha-keto pyruvic acid have been investigated by using hybrid density functional theory. The calculated geometries and the corresponding vibrational spectra of the three stable monomer conformers are found to be in good accord with earlier results. The present work provides the first detailed structure and vibrational analysis of the two stable dimer conformers, one of which is consistent with the X-ray diffraction and spectroscopic data, and also shows that there is only one stable form for the radical, with the others likely dissociated to the acetyl radical. (C) 2003 Elsevier B.V. All rights reserved.