Vibrational spectroscopy of 2-pyridone and its clusters in supersonic jets: Structures of the clusters as revealed by characteristic shifts of the NHand C=O bands

Vibrational spectroscopy of the key functional vibrations of 2-pyridone and its hydrogen-bonded clusters with water, methanol, dioxane, dimethylether, as well as its dimer, has been carried out by using infrared-ultraviolet ( IR-UV) and stimulated Raman-UV double resonance methods combined with fluor escence detection. The characteristic spectral changes upon the cluster for mation have been observed for the NH and C=O stretching vibrations of the b are molecule and also for the OH stretching vibrations of the solvent molec ules. The cluster structures were investigated by comparing the observed sp ectra with the simulated ones of the energy-optimized structures obtained b y ab-initio molecular orbital calculations. It was found that the "ring-typ e'' hydrogen-bonded structure is appropriate for the cluster with water or methanol, while the "linear-type'' hydrogen-bonded structure is appropriate for the cluster with dioxane or dimethylether. The symmetric form of 2-pyr idone dimer was confirmed by the observed spectra, as well as the ab-initio calculation. A clear correlation between the observed frequency shifts of the NH stretching vibrations and the calculated NH ... O hydrogen-bond angl es was obtained indicating that the hydrogen-bond angle distortion reduces the local hydrogen-bond strength. Also it was found the blue shifts of the origin bands of the S-1<--S-0 electronic transition strongly depends on the type of the cluster structures. (C) 1999 American Institute of Physics. [S 0021-9606(99)01017-X].