Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin , Madison, Wisconsin 53706, United States.
J Phys Chem B. 2013 Dec 12;117(49):15536-44. doi: 10.1021/jp405860u. Epub 2013 Aug 28.
It is well-known that in ice Ih the oxygen atoms form a regular hexagonal lattice while the positions of the hydrogen atoms are disordered, called proton disorder in the literature. Various OH (OD) stretch vibrational spectroscopies (e.g., IR, Raman, two-dimensional IR (2DIR), and hole burning) have been used to probe this proton disorder in the past several decades. However, the presence and the magnitude of the inhomogeneous broadening due to this proton disorder in the vibrational spectroscopy is still controversial. In this work, we calculate 2DIR spectroscopy for HOD in D2O ice Ih at 80 K with a mixed quantum/classical approach, and make comparison to a recent 2DIR experiment on the same system. Fair agreement is achieved between theory and experiment, although the calculated 2DIR line shape shows inhomogeneous broadening that was not observed in the experiment. However, the theory reproduces the linear IR for the same system fairly well, and the inhomogeneous broadening from the calculation is consistent with the extrapolation of the experimental IR line-widths in the literature. The effect of this proton disorder on the 2DIR line shape is explored in detail. We also calculate the vibrational three-pulse photon echo peak shift signal, which shows signatures of both low-frequency dynamics and inhomogeneous broadening.
众所周知，在冰 Ih 中，氧原子形成规则的六方晶格，而氢原子的位置是无序的，在文献中称为质子无序。过去几十年中，各种 OH（OD）伸缩振动光谱学（例如 IR、Raman、二维 IR（2DIR）和孔烧蚀）已被用于探测这种质子无序。然而，由于这种质子无序在振动光谱中存在的不均匀展宽及其大小仍然存在争议。在这项工作中，我们使用混合量子/经典方法计算了 80 K 下 D2O 冰 Ih 中 HOD 的 2DIR 光谱，并与同一系统的最新 2DIR 实验进行了比较。理论与实验之间达成了很好的一致性，尽管计算出的 2DIR 线宽显示出实验中未观察到的不均匀展宽。然而，该理论很好地再现了相同体系的线性 IR，并且计算出的不均匀展宽与文献中实验 IR 线宽的外推一致。详细探讨了这种质子无序对 2DIR 线宽的影响。我们还计算了振动三脉冲光子回波峰位移信号，该信号显示出低频动力学和不均匀展宽的特征。
