Structures and vibrations of 2-naphthol-(NH3)(n) (n=1-3) hydrogen-bonded clusters investigated by IR-UV double-resonance spectroscopy

OH and NH stretching vibrations of 2-naphthol-(NH3)(n) (n = 1-3) hydrogen ( H)-bonded clusters in the electronic ground state have been observed by IR- UV double-resonance spectroscopy. Cluster size dependence of the OH stretch ing vibration was investigated by comparing the observed spectra with the s imulated ones obtained by ab initio molecular orbital calculations at the H F/6-31G and HF/6-31G(d,p) level. For the n = 1 cluster, having the trans-li near structure, the band of the H-bonded OH stretching vibration exhibits a remarkably large low-frequency shift as large as 400 cm(-1) from that of b are 2-naphthol. For the n = 2 and 3 clusters, having a ring-form of hydroge n bonds, the band of the OH stretching vibration showed further large redsh ifts (similar to 700 cm(-1)). In addition, the largely red-shifted bands be come extremely broad. The results represent the extensive overlap of many b ands which appeared by anharmonic coupling with the OH stretching vibration , IVR process. (C) 2000 Elsevier Science B.V. All rights reserved.