Danish Hydrocarbon Research and Technology Centre, Technical University of Denmark, Elektrovej 375, 2800 Kgs. Lyngby, Denmark.
Department of Chemistry, Technical University of Denmark, Kemitorvet 206, 2800 Kgs. Lyngby, Denmark.
J Chem Phys. 2022 Feb 28;156(8):084305. doi: 10.1063/5.0081161.
The specific far-infrared spectral signatures associated with highly localized large-amplitude out-of-plane librational motion of water molecules have recently been demonstrated to provide sensitive spectroscopic probes for the micro-solvation of organic molecules [Mihrin et al., Phys. Chem. Chem. Phys. 21(4), 1717 (2019)]. The present work employs this direct far-infrared spectroscopic approach to investigate the non-covalent intermolecular forces involved in the micro-solvation of a selection of seven ether molecules with systematically varied alkyl substituents: dimethyl ether, diethyl ether, diisopropyl ether, ethyl methyl ether, t-butyl methyl ether, and t-butyl ethyl ether. The ranking of the observed out-of-plane water librational band signatures for this selected series of ether-water complexes embedded in inert neon matrices at 4 K reveals information about the interplay of directional intermolecular hydrogen bond motifs and non-directional and long-range dispersion interactions for the micro-solvated structures. These far-infrared observables differentiate minor subtle effects introduced by specific alkyl substituents and serve as rigorous experimental benchmarks for modern quantum chemical methodologies of various levels of scalability, which often fail to accurately predict the structural variations and corresponding vibrational signatures of the closely related systems. The accurate interaction energies of the series of ether-water complexes have been predicted by the domain based local pair natural orbital coupled cluster theory with single-, double-, and perturbative triple excitations, followed by a local energy decomposition analysis of the energy components. In some cases, the secondary dispersion forces are in direct competition with the primary intermolecular hydrogen bonds as witnessed by the specific out-of-plane librational signatures.
水分子大振幅面外摆动的特定远红外光谱特征最近已被证明是对有机分子微溶剂化的敏感光谱探针[Mihrin 等人，Phys. Chem. Chem. Phys. 21(4), 1717 (2019)]。本工作采用这种直接远红外光谱方法，研究了一系列具有系统变化的烷基取代基的七种醚分子的微溶剂化中非共价分子间力：二甲醚、二乙醚、二异丙醚、乙基甲基醚、叔丁基甲基醚和叔丁基乙基醚。在 4 K 下惰性氖基质中嵌入的所选醚-水配合物的观察到的面外水分子摆动带特征的排序揭示了关于微溶剂化结构中定向分子间氢键模式和非定向和远程色散相互作用相互作用的信息。这些远红外可观察量区分了由特定烷基取代基引入的微小细微效应，并作为各种可扩展性水平的现代量子化学方法的严格实验基准，这些方法往往无法准确预测密切相关体系的结构变化和相应的振动特征。通过基于域的局部对自然轨道耦合簇理论，采用单、双和微扰三重激发对一系列醚-水配合物的准确相互作用能进行了预测，随后对能量成分进行了局部能量分解分析。在某些情况下，二次色散力与主要的分子间氢键直接竞争，这可以从特定的面外摆动特征中看出。
