Observation of OH stretching vibrations of hydrogen-bonded molecular clusters

在超声射流中观察到了尺寸选择性的芳基醇氢键团簇的OH伸缩振动。采用了两种光谱方法：红外-紫外双共振和受激拉曼-紫外双共振光谱。所研究的氢键体系有苯酚-（H_2O）_n、萘酚-（H_2O）_n、环庚三烯酚酮-（H_2O）_n以及与其它碱分子的团簇，在苯酚-（H_2O）_n团簇（n=1-5）中，不仅观察到了苯酚中心的~ vOH，而且还观察到了水中心的~ vOH。通过与从头算分子轨道计算结果的比较，研究了簇合物的结构。结果表明，对于2n 4的团簇，环状氢键结构是最稳定<less than or equal><less than or equal>的，而对于较大尺寸的团簇，与环状结构不同的异构体似乎变得稳定。萘酚-（H_2O）_n簇合物的OH伸缩谱与苯酚-（H_2O）_n簇合物的OH伸缩谱基本相同，并提出了类似的簇合物结构。研究了氢键的形成导致的^vOH频率随碱性强度的降低，发现这种降低与碱分子的质子亲合势有很好的相关性。

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.