Physikalisch-Chemisches Institut, Universität Zürich, Zürich, Switzerland.
J Chem Phys. 2013 Jul 7;139(1):014501. doi: 10.1063/1.4812216.
Using three-dimensional infrared (3D-IR) spectroscopy, we investigate the vibrational dynamics of isotope-diluted ice Ih. By probing the OD stretch mode of HOD in H2O, we observe an extremely rapid decay (≈200 fs) of the population from the second vibrational excited state. Quantum simulations based on a two-dimensional Lippincott-Schroeder potential agree nearly quantitatively with the experimental 3D-IR lineshapes and dynamics. The model suggests that energy dissipation is enhanced due to nonadiabatic effects between vibrational states, which arise from strong mode-mixing between the OD stretch mode with lattice degrees of freedom. Furthermore, we compare the simulation results to ab initio based potentials, in which the hydrogen bond anharmonicity is too small to reproduce the experimental 3D-IR spectra. We thus conclude that the Lippincott-Schroeder potential effectively coalesces many degrees of freedom of the crystal into one intermolecular coordinate.
利用三维红外（3D-IR）光谱，我们研究了同位素稀释冰 Ih 的振动动力学。通过探测 H2O 中 HOD 的 OD 伸缩模式，我们观察到第二振动激发态的布居数非常迅速地衰减（≈200fs）。基于二维 Lippincott-Schroeder 势的量子模拟与实验 3D-IR 线形状和动力学几乎完全吻合。该模型表明，由于振动态之间的非绝热效应，能量耗散增强，这是由于 OD 伸缩模式与晶格自由度之间的强烈模式混合所致。此外，我们将模拟结果与基于从头算的势进行了比较，其中氢键的非谐性太小，无法重现实验的 3D-IR 光谱。因此，我们得出结论，Lippincott-Schroeder 势有效地将晶体的多个自由度合并为一个分子间坐标。
