通过振动极化激元选择性激发IR非活性模式：来自原子尺度模拟的洞见
Selective Excitation of IR-Inactive Modes via Vibrational Polaritons: Insights from Atomistic Simulations
AI总结：
本研究利用经典腔分子动力学模拟液态甲烷的振动强耦合，发现泵浦上极化激元可选择性激发IR非活性对称弯曲模式，并揭示光-物质杂化程度决定能量转移效率。
摘要：
振动极化激元是分子振动与红外（IR）腔模之间形成的光-物质杂化态，为改变化学反应路径和能量转移过程提供了一种新途径。对于涉及凝聚相分子的振动极化激元，较短的极化激元寿命引发了争论：与在自由空间或弱耦合条件下直接激发分子相比，泵浦极化激元是否会对分子产生不同影响。在此，针对处于振动强耦合下的液态甲烷，经典腔分子动力学模拟表明，泵浦由甲烷非对称弯曲模式形成的上极化激元（UP）有时能够选择性激发IR非活性的对称弯曲模式。当分子体系分别采用经验力场和机器学习势描述时，这一发现在两种情况下均得到验证，并且与基于Fermi黄金规则计算的极化激元能量转移速率解析理论在定性上一致。此外，本研究表明，当UP同时具有来自光子和分子的显著贡献时，极化激元诱导的向IR非活性模式的能量转移达到最大效率，这突显了光-物质杂化的重要性。由于IR非活性振动模式通常无法通过直接IR激发触及，本研究强调了极化激元形成在选择性控制IR非活性振动方面的独特作用。由于这种极化激元诱导过程发生在极化激元衰减之后，它可能在长于极化激元寿命的时间尺度上影响IR光化学，正如实验中所观察到的那样。
英文摘要：
Vibrational polaritons, hybrid light-matter states formed between molecular vibrations and infrared (IR) cavity modes, provide a novel approach for modifying chemical reaction pathways and energy transfer processes. For vibrational polaritons involving condensed-phase molecules, the short polariton lifetime raises debate over whether pumping polaritons may produce different effects on molecules compared to directly exciting the molecules in free space or under weak coupling. Here, for liquid methane under vibrational strong coupling, classical cavity molecular dynamics simulations show that pumping the upper polariton (UP) formed by the asymmetric bending mode of methane can sometimes selectively excite the IR-inactive symmetric bending mode. This finding is validated when the molecular system is described using both empirical force fields and machine-learning potentials, also in qualitative agreement with analytical theory of polariton energy transfer rates based on Fermi's golden rule calculations. Additionally, our study suggests that polariton-induced energy transfer to IR-inactive modes reaches maximal efficiency when the UP has significant contributions from both photons and molecules, underscoring the importance of light-matter hybridization. As IR-inactive vibrational modes are generally inaccessible to direct IR excitation, our study highlights the unique role of polariton formation in selectively controlling IR-inactive vibrations. Since this polariton-induced process occurs after the polariton decays, it may impact IR photochemistry on a timescale longer than the polariton lifetime, as observed in experiments.
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