Terahertz spectroscopy and molecular modeling of 2-pyridone clusters

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.