Vibrational Spectroscopy of Ion Solvent Clusters

实验物理化学项目支持加州理工学院Mitchio Okumura继续阴离子团簇溶剂化的研究。具体来说，他利用振动预解离光谱研究了与“n”水分子水合的各种阴离子的结构，作为n的函数。显然，对阳离子水合物簇和与稀有气体聚集的阴离子的实验研究表明，溶剂化壳形成，离子在内部。另一方面，卤化物阴离子水合物团簇的理论研究表明，离子与团簇水分子的表面结合，随着团簇大小的增加，发生从表面溶剂化到内部溶剂化的转变。Okumura将专注于氢拉伸区域；这一区域的频移和线宽可以帮助我们了解离子和溶剂分子之间以及溶剂分子之间的氢键。此外，双光子光谱（红外-红外双共振预解或红外-紫外振动辅助光分离）将对那些结合更强的团簇产生影响。最后，将研究与平流层气溶胶化学有关的酸的团簇溶剂化。将进行从头开始的理论努力，以帮助确定簇的几何形状。虽然这项工作的目的是在基础水平上研究离子-溶剂相互作用，但第二个动机是阐明与大气化学相关的溶剂化过程和离子反应机制。许多将被研究的系统在发生在平流层和对流层的非均相反应中起中心作用。这些离子水合物与大气物质（如硝酸和盐酸）的加合物可以作为大气气溶胶吸附和离子解离的中间体模型。

The Experimental Physical Chemistry Program supports Mitchio Okumura of California Institute of Technology in his continuing studies on anionic cluster solvation. Specifically, he uses vibrational predissociation spectroscopy to study the structure of various anions hydrated with `n` molecules of water, as a function of n. Apparently, experimental studies on cationic hydrate clusters and anions clustered with rare gases indicate that solvation shells form and the ion is in the interior. Theoretical work on halide anionic hydrate clusters suggest, on the other hand, that the ion is bound to the surface of clustered water molecules, and as the cluster size increases, a transition from surface- to interior-solvation occurs. Okumura will focus on the hydrogen stretching region; the frequency shifts and linewidths in this region should yield insight on hydrogen bonding both between ion and solvent molecules and among solvent molecules. In addition, two photon (infrared-infrared double resonance predissociation or infrared-ultraviolet vibrationally assisted photodetachment) spectroscopy will be brought to bear on those clusters that are more strongly bound. Finally, cluster solvation of acids implicated in stratospheric aerosol chemistry will be investigated. An ab initio theoretical effort will be carried out to aid in determining cluster geometries. While the aim of this work is to investigate ion-solvent interactions at a fundamental level, a second motivation is to elucidate solvation processes and ionic reaction mechanisms of relevance to atmospheric chemistry. Many of the systems that will be investigated play central roles in heterogeneous reactions occuring in the stratosphere and troposphere. Adducts of these ionic hydrates with atmospheric species such as nitric acid and hydrochloric acid may serve as models of intermediates in the adsorption and ionic dissociation on atmospheric aerosols.