The Interplay Between Local H-bond Vibrations and Lattice Dynamics in Organic Crystals
Noam Pinsk a, Omer Yaffe a
a Weizmann Institute of Science, Herzl St. 234, Rehovot 7610001, Israel
Proceedings of Dynamic Materials, Crystals and Phenomena Conference (DynaMIC23)
Fribourg, Switzerland, 2023 March 22nd - 24th
Organizers: Jovana Milic and Simon Krause
Poster, Noam Pinsk, 022
Publication date: 15th February 2023

In a hydrogen bond (H-bond), adjacent electronegative atoms/groups share a proton that has two distinct equilibrium positions. Though H-bonds are abundant in organic crystals, there is little understanding of how their local dynamics influence the collective lattice motion. We expect H-bonded crystals to have inherent metastable states that stem from the proton motion between its equilibrium positions. In this project, I test the hypothesis that H-bonded crystals have unique structural dynamics that combine the proton's motion and the crystal's lattice dynamics. Using state-of-the-art THz-Raman spectroscopy, I investigate the temperature evolution of both inter- and intra-molecular modes in alpha-glycine crystals. Despite the simple structure and absence of known phase transitions, I show that specific lattice modes behave anomalously with temperature. These anomalies are absent in Anthracene that is bound only by Van der Waals interactions. My study is a first step towards elucidating how metastable states in the macroscopic system emerge from fundamental interactions such as the H-bond.

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