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MO: Fachverband Molekülphysik

MO 22: Ultrafast Dynamics III

MO 22.2: Talk

Thursday, March 13, 2025, 11:15–11:30, HS XVI

Linear and Two-Dimensional IR Spectroscopy of an Isotopically Labeled Multifunctional Vibrational Probe — •Claudia Gräve, Jörg Lindner, Stefan Flesch, Luis Ignacio Domenianni, and Peter Vöhringer — Clausius-Institute, University of Bonn, Wegelerstr. 12, 53115 Bonn, Germany

Vibrational spectroscopy of biomacromolecules often relies on the introduction of infrared probes, whose vibrations are highly sensitive to the local environment. Here, we report on the prospective IR probe, 3-(4-azidophenyl)propiolonitrile, which contains several IR-active functional groups.

Its linear FTIR spectrum is highly perturbed in the spectral region of the asymmetric azide stretching fundamental due to the presence of Fermi resonances. We managed to assign the fundamental transition via isotope labeling of the azide group. In combination with DFT calculations, this allowed us to construct a two-tiered Fermi resonance Hamiltonian to identify the involved combination tones.

Additionally, we performed ultrafast vibrational spectroscopy on the isotopically labeled IR probe. 2D-IR spectra exhibit a delayed appearance of cross-peaks between the azide asymmetric and the in-phase propiolonitrile stretching modes. Along with narrowband IR-pump/IR-probe spectroscopy, these results reveal an irreversible intramolecular vibrational energy redistribution (IVR) that involves couplings of the two oscillators to different subsets of low-frequency modes. Our data shows a time constant of 2.3 ps for the IVR, whereas energy dissipation to the solvent occurs on a time scale of 18 ps.

Keywords: 2D-IR spectroscopy; Fermi resonance; vibrational probe; isotope labeling