Observation of OH stretching vibrations of hydrogen-bonded molecular clusters

点击翻译按钮获取中文摘要

The OH stretching vibrations of size-selected hydrogen-bonded clusters of aryl alcohols were observed in supersonic jets. Two spectroscopic methods were applied ; IR-UV double resonance and stimulated Raman-UV double resonance spectroscopies. The investigated hydrogen-bonded systems are phenol-(H_2O)_n, naphthol-(H_2O)_n, tropolone-(H_2O)_n, and also the clusters with other base molecules.In phenol-(H_2O)_n clusters (n=1-5), not only ^vOH of the phenol site but also of the water sites were observed. The cluster structures were investigated by comparing the observed spectra with the ones obtained by ab initio molecular orbital calulation. It was found that ring form hydrogen-bonded structure is most stable for the clusters with 2<less than or equal>n<less than or equal>4, and for larger size clusters, isomers different from the ringstructure seems to becomestable. The OH stretching spectra of naphthol-(H_2O)_n clusters are essentially the same with those of phenol-(H_2O)_n and a similar cluster structures are suggested. It was also found that the relaxation rate of the hydrogen bonded ^vOH are much larger than that of ^vOH free from the hydrogen bondThe decrease of ^vOH frequency by the hydrogen-bond formation versus the strength of basicity was investigated nad it was found the increase shows good correlation with the proton affinity of the base molecules.