Deconstructing water’s diffuse OH stretching vibrational spectrum with cold clusters
Deconstructing water’s diffuse OH stretching vibrational spectrum with cold clusters
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DOI：
10.1126/science.aaw4086
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发表时间：
2019-04
期刊：
影响因子：
56.9
通讯作者：
Nan Yang;Chinh H. Duong;P. Kelleher;A. McCoy;Mark A. Johnson
中科院分区：
文献类型：
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作者：
Nan Yang;Chinh H. Duong;P. Kelleher;A. McCoy;Mark A. Johnson
原则上，水（H2O）的表面结构应该可以从O-H振动中辨别出来。然而，在实际操作中，如此多的配置会迅速相互转换，以至于频段非常宽。Yang等人使用同位素体研究了一个铯离子周围的20个H2O簇，这些同位素体在19个重水（D2O）分子中改变了一个H2O的位置。精确分配的光谱特征可以很好地映射到整体表面光谱上。《科学》，本期第275页。在19个D2O分子中，一个H2O分子的不同位置的簇的光谱有助于解释水的总体表面光谱。水所显示的扩散振动包络阻止了对不同氢键拓扑结构如何决定单个羟基（OH）振荡子的光谱响应的直接观察。利用冷的、同位素标记的簇离子，我们报道了在Cs+·（D2O）20离子采用的笼状笼状结构中嵌入不同位置的单个完整水分子的光谱特征。这些模式揭示了同一水分子上两个OH基团频率之间的位点依赖相关性，并确定了自由OH基团的结合OH伴侣只占光谱低能区的波段。观察到的多重结构揭示了基本面的均匀线宽，并量化了耦合对分子内弯曲和分子间软模式产生的非调和贡献。
Wet surface sightings in clusters In principle, the surface structure of water (H2O) should be discernable from the O–H vibrations. In practice, however, so many configurations rapidly interconvert that the bands are bewilderingly broad. Yang et al. studied a cluster of 20 H2O surrounding a cesium ion, using isotopomers that vary in the position of one H2O amid 19 heavy water (D2O) molecules. Precisely assigned spectral features from contributing configurations mapped well onto a bulk surface spectrum. Science, this issue p. 275 Spectra of clusters with varied positioning of one H2O amid 19 D2O molecules help explain the bulk water surface spectrum. The diffuse vibrational envelope displayed by water precludes direct observation of how different hydrogen-bond topologies dictate the spectral response of individual hydroxy group (OH) oscillators. Using cold, isotopically labeled cluster ions, we report the spectral signatures of a single, intact water (H2O) molecule embedded at various sites in the clathrate-like cage structure adopted by the Cs+·(D2O)20 ion. These patterns reveal the site-dependent correlation between the frequencies of the two OH groups on the same water molecule and establish that the bound OH companion of the free OH group exclusively accounts for bands in the lower-energy region of the spectrum. The observed multiplet structures reveal the homogeneous linewidths of the fundamentals and quantify the anharmonic contributions arising from coupling to both the intramolecular bending and intermolecular soft modes.