Dzugan Laura C, DiRisio Ryan J, Madison Lindsey R, McCoy Anne B
Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.
Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
Faraday Discuss. 2018 Dec 13;212(0):443-466. doi: 10.1039/c8fd00120k.
Couplings involving large amplitude vibrations in H+(H2O)n (n = 1-4) are explored using several theoretical approaches. These include harmonic treatments, analysis of harmonically coupled anharmonic oscillator (HCAO) models of the OH stretching vibrations, vibrational perturbation theory (VPT2) in internal coordinates, and diffusion Monte Carlo (DMC). It is found that couplings between shared proton stretches and HOH bends can lead to normal modes that are significantly mixed in character. Couplings between the various OH stretching vibrations are much weaker, and the OH stretches are well-described by harmonically coupled anharmonic oscillator models. Anharmonic couplings and the role of these large amplitude vibrations are further explored using DMC and VPT2. Based on the results of these calculations, it is found that all of the H+(H2O)n ions considered in this study display several different types of large amplitude vibrational motions even in their ground states. In the case of H7O3+, degenerate VPT2 calculations indicate that there are large couplings between the shared proton stretch and various lower frequency vibrations that correspond to motions that break the ionic hydrogen bonds. This leads to vibrational eigenstates that have contributions from several zero-order states.
使用几种理论方法研究了H+(H2O)n（n = 1 - 4）中涉及大幅度振动的耦合。这些方法包括谐波处理、OH伸缩振动的谐波耦合非谐振子（HCAO）模型分析、内坐标中的振动微扰理论（VPT2）以及扩散蒙特卡罗（DMC）。研究发现，共享质子伸缩与HOH弯曲之间的耦合可导致特征上显著混合的正常模式。各种OH伸缩振动之间的耦合要弱得多，并且OH伸缩可以通过谐波耦合非谐振子模型很好地描述。使用DMC和VPT2进一步探索了非谐耦合以及这些大幅度振动的作用。基于这些计算结果，发现本研究中考虑的所有H+(H2O)n离子即使在基态也表现出几种不同类型的大幅度振动运动。在H7O3+的情况下，简并VPT2计算表明，共享质子伸缩与各种对应于破坏离子氢键运动的低频振动之间存在很大的耦合。这导致振动本征态具有几个零阶态的贡献。
