Spectroscopic study of novel cluster structures created as chemical intermediates in supersonic molecular beams

对下列体系进行了喷冷分子簇阳离子的光谱研究：1.[C_6H_6(NH_3)_n]^+(n=1和2)的红外光谱和电子光谱表明，它们的稳定形式是S络合物，其中的氨基与苯基形成共价键，作为芳烃亲核取代的反应中间体。结合量子化学计算，研究了[苯-(甲醇)_n]^+(n=2，3)的相似结构。用红外光谱研究了H^+(H2O)n(n=20-200)的氢键网络结构。结果发现，随着团簇尺寸的增大，团簇的光谱特征变得类似于水和冰的特征，表明大尺寸团簇的网络形态逐渐转变为块体系统的网络形态。用真空-紫外单光子电离红外光谱研究了丙酮和醋酸的中性和阳离子簇合物的结构。研究发现，许多团簇的酮-烯醇转变是在电离后产生的，例如它们的二聚体，而它们的中性分子是酮式的。讨论了异构化机理与它们的质子亲和力和质子转移坐标势面的关系。

Spectroscopic studies on jet-cooled molecular cluster cations have been carried out for the following systems ;1. IR and electronic spectroscopy of [C_6H_6(NH_3)_n]^+ (n=1 and 2) revealed that their stable forms are of s-complex type, in which the ammonia moiety is covalently bonded to the benzene moiety as expected as the reaction intermediate of nucleophilic substitution of aromatics. The similar structures of [Benzene-(Methanol)_n]^+ (n=2, 3) were also investigated in combination with quantum chemical calculations.2. H-bond network structures of H^+(H_2O)_n (n=20-200) were investigated by IR spectroscopy. It was found that the spectral features of the clusters with increasing cluster size become similar to the characteristic features of water and of ice, indicating the network morphology of the large-size clusters transmutes gradually to those of the bulk systems. It was also found that the spectral feature depends on the internal energy in the species.3.Structures of neutral and cationic clusters of acetone and of acetic acid were investigated by using IR spectroscopy based on vacuum-ultraviolet one-photon ionization detection. It was found that the keto-enol transition is generated after the ionization for many clusters, such as their dimers, whereas their neutrals are of the keto-form. The isomerization mechanism was discussed in relation to their proton affinities and the potential surface of the proton-transfer coordinate.