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Updated: Jun 2, 2025

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Distinct Fermi Resonance Patterns of Weak Coupling in 2D-IR Spectra of 5-Cyanoindole Revealed by Isotope Labeling
Bingyao Wang1, Yanan Dong2, Zhiyuan Zhao1
1Center for Ultrafast Science and Technology, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
Abstract:
Fermi resonance is a common phenomenon, and a hidden caveat exists in the applications of infrared probes, causing spectral complication and shorter vibrational lifetime. In this work, using the cyanotryptophan (CNTrp) side chain model compound 5-cyanoindole (CN-5CNI), we performed Fourier transform infrared spectroscopy (FTIR) and two-dimensional infrared (2D-IR) spectroscopy on unlabeled 12C14N-5CNI and its isotopically labeled substituents (12C15N-5CNI, 13C14N-5CNI, 13C15N-5CNI) and demonstrated the existence of Fermi resonance in 5CNI. By constructing the Hamiltonian and simulating 2D-IR spectra, we show that the distinct Fermi resonance 2D-IR patterns in various isotope substituents are determined by the quantum mixing consequences at the v = 1 state, as well as the v = 2 state, where the Fermi coupling and anharmonicity play a crucial role. Our work provides important insights into the elusive type of Fermi resonance, where the coupling is much smaller than the anharmonicity, which is termed the weak coupling case.
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