Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093.
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093.
Proc Natl Acad Sci U S A. 2018 May 8;115(19):4845-4850. doi: 10.1073/pnas.1722063115. Epub 2018 Apr 19.
We report experimental 2D infrared (2D IR) spectra of coherent light-matter excitations--molecular vibrational polaritons. The application of advanced 2D IR spectroscopy to vibrational polaritons challenges and advances our understanding in both fields. First, the 2D IR spectra of polaritons differ drastically from free uncoupled excitations and a new interpretation is needed. Second, 2D IR uniquely resolves excitation of hybrid light-matter polaritons and unexpected dark states in a state-selective manner, revealing otherwise hidden interactions between them. Moreover, 2D IR signals highlight the impact of molecular anharmonicities which are applicable to virtually all molecular systems. A quantum-mechanical model is developed which incorporates both nuclear and electrical anharmonicities and provides the basis for interpreting this class of 2D IR spectra. This work lays the foundation for investigating phenomena of nonlinear photonics and chemistry of molecular vibrational polaritons which cannot be probed with traditional linear spectroscopy.
我们报告了相干光物质激发——分子振动极化激元的实验二维红外（2D IR）光谱。将先进的 2D IR 光谱学应用于振动极化激元，在这两个领域都挑战和推进了我们的理解。首先，极化激元的 2D IR 光谱与自由非耦合激发有很大的不同，需要新的解释。其次，2D IR 以一种选择性的方式独特地分辨出混合光物质极化激元和意想不到的暗态的激发，揭示了它们之间隐藏的相互作用。此外，2D IR 信号突出了分子非谐性的影响，这种影响适用于几乎所有的分子系统。我们开发了一个量子力学模型，它包含了核和电非谐性，并为解释这一类 2D IR 光谱提供了基础。这项工作为研究非线性光子学和分子振动极化激元的化学反应现象奠定了基础，这些现象是传统线性光谱学无法探测到的。
