The terahertz (10-140 cm(1)) spectrum of 2-pyridone (2PD) in a carbon tetrachloride solution has been recorded and simulated using both MP2 and DFT methods. The calculated structures, spectra, and binding energies reveal that the strong absorption at 109 cm(1) arises from an intermolecular in-plane rocking of the 2PD dimer. Yet there is additional intensity in the 2PD experimental spectrum that is not accounted for by theoretical predictions of the dimer alone. A hydrogen-bonded 2PD tetramer may be the source of this anomalous intensity and calculations of the proposed structure and vibrations are presented. (C) 2008 Elsevier B.V. All rights reserved.