Ground state properties and infrared spectra of anharmonic vibrational polaritons of small molecules in cavities
Ground state properties and infrared spectra of anharmonic vibrational polaritons of small molecules in cavities
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DOI：
10.1063/5.0040853
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发表时间：
2021-03-14
影响因子：
4.4
通讯作者：
Saalfrank, Peter
中科院分区：
文献类型：
--
作者：
Fischer, Eric W.;Saalfrank, Peter
最近的实验和理论表明，分子的基态性质和反应性可以被修改时，放置在一个纳米级的腔，引起振动模式和量子化腔场之间的强耦合。这通常被认为是由腔扭曲的玻恩-奥本海默基态势或由光-物质混合态，振动极化激元的形成引起的。在这里，我们系统地研究了腔的基态性质和红外光谱的单分子，考虑振动腔耦合强度从零到振动超强耦合制度的影响。分别使用Li-H和O-H伸缩模式和NH3反转模式的单模模型，将与振动跃迁共振的单腔模式耦合到位置相关的分子偶极函数。我们解决的腔模式上的极化激元基态能量，平衡键长，离解能，异构化的活化能，和振动极化激元红外光谱的影响。在协议与早期的工作，我们观察到所有提到的性能受到强烈影响的腔，但只有当偶极自能贡献的相互作用哈密顿量被忽略。当包括该术语时，这些性质不再显著地依赖于耦合。相反，振动极化激元红外光谱总是受到腔模的影响，这是由于激发的振动极化激元的形成。有人认为，振动极化激元的量子化性质是关键，不仅解释分子光谱的腔，但也了解实验观察到的修改腔中的分子反应性。
Recent experiments and theory suggest that ground state properties and reactivity of molecules can be modified when placed inside a nanoscale cavity, giving rise to strong coupling between vibrational modes and the quantized cavity field. This is commonly thought to be caused either by a cavity-distorted Born-Oppenheimer ground state potential or by the formation of light-matter hybrid states, vibrational polaritons. Here, we systematically study the effect of a cavity on ground state properties and infrared spectra of single molecules, considering vibration-cavity coupling strengths from zero up to the vibrational ultrastrong coupling regime. Using single-mode models for Li-H and O-H stretch modes and for the NH3 inversion mode, respectively, a single cavity mode in resonance with vibrational transitions is coupled to position-dependent molecular dipole functions. We address the influence of the cavity mode on polariton ground state energies, equilibrium bond lengths, dissociation energies, activation energies for isomerization, and on vibro-polaritonic infrared spectra. In agreement with earlier work, we observe all mentioned properties being strongly affected by the cavity, but only if the dipole self-energy contribution in the interaction Hamiltonian is neglected. When this term is included, these properties do not depend significantly on the coupling anymore. Vibro-polaritonic infrared spectra, in contrast, are always affected by the cavity mode due to the formation of excited vibrational polaritons. It is argued that the quantized nature of vibrational polaritons is key to not only interpreting molecular spectra in cavities but also understanding the experimentally observed modification of molecular reactivity in cavities.