Infrared-induced coherent vibration of a hydrogen-bonded system: Effects of mechanical and electrical anharmonic couplings
Infrared-induced coherent vibration of a hydrogen-bonded system: Effects of mechanical and electrical anharmonic couplings
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DOI：
10.1063/1.3181777
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发表时间：
2009-07-28
影响因子：
4.4
通讯作者：
Tahara, Tahei
中科院分区：
文献类型：
--
作者：
Ishii, Kunihiko;Takeuchi, Satoshi;Tahara, Tahei
利用超短红外抽运-可见光探测光谱技术研究了分子内氢键分子醌茜的红外诱导低频相干振动，时间分辨率约为60 fs。在该实验中，对称OH伸缩模的IR激发诱导低频振动相干性，然后将其检测为可见光吸收强度的振荡。通过基于密度泛函理论（DFT）的振动分析，将所观察到的振动归因于“氢键调制”振动。由于红外激发的振动相干性形成需要大量的非谐耦合，我们进行了基于DFT的数值分析的OH伸缩和低频模式之间的非谐耦合，通过评估的组合带的过渡时刻。我们考虑了两种类型的非和谐性，即，机械非谐性和电非谐性。虽然电非谐性常常被忽略，但发现电非谐性对该系统中低频模式的振动相干性的产生具有与机械非谐性相当的贡献。这一结果表明，在强氢键系统的电非谐性的普遍重要性。
We have studied IR-induced low-frequency coherent vibration of an intramolecularly hydrogen-bonded molecule, quinizarin, by an ultrashort IR-pump-visible-probe spectroscopy with similar to 60 fs time resolution. In this experiment, the IR excitation of the symmetric OH-stretching mode induced a low-frequency vibrational coherence, which was then detected as an oscillation of the visible absorption intensity. The observed oscillation was assigned to a "hydrogen-bond modulating" vibration by the vibrational analysis based on the density functional theory (DFT). Because the vibrational coherence formation by IR excitation requires a substantial anharmonic coupling, we carried out a DFT-based numerical analysis of the anharmonic coupling between the OH-stretching and the low-frequency mode, by evaluating the transition moment of the combination band. We took account of two types of anharmonicities, i.e., the mechanical anharmonicity and the electrical anharmonicity. Although the electrical anharmonicity is often neglected, it was found that the electrical anharmonicity had a comparable contribution to the mechanical anharmonicity, in generation of vibrational coherence of the low-frequency mode in this system. This result indicates general importance of the electrical anharmonicity in strongly hydrogen-bonded systems.