Chemistry

High-resolution IR spectroscopy reveals new insights into hydrogen bonding in hydrogen sulfide

Far-infrared spectrum of H2S-H2S at T = 0.37 K calculated using ab initio intermolecular potentials and dipole functions. Credit: Nature Communications (2024). DOI: 10.1038/s41467-024-53444-6

At first glance, water and the foul-smelling molecule hydrogen sulfide don’t seem to have much in common. However, if you invest a little energy, some differences will disappear.

At first glance, the smell of soft drink ice cubes and grandma’s famous egg salad might not seem to have much in common. However, from a chemical perspective, the underlying molecules water (H2O) and hydrogen sulfide (H2S) are not very similar. The bonding of hydrogen in one water molecule with oxygen in another water molecule has been studied in great detail.

But the question of whether its larger sibling, H2S, behaves similarly is less well understood. A new study from the Bochum Cluster of Excellence, “Ruhr Explores Solvation” (RESOLV), fills this gap. The team from Germany’s Ruhr University Bochum Physical Chemistry 2 and their colleagues published their findings in the journal Nature Communications on November 5, 2024.

Experimental work by Professor Martina Havenith’s Bochum group was complemented by theoretical work by Professor Joel Bowman of Emory University in Atlanta and Professor Ad van der Avoird of Radboud University in Nijmegen.

H2S is one of the most primitive sulfur-containing molecules in the interstellar medium and is thought to be an important part of various biological processes in mammals. Although the chemical community investigated H2S in several infrared studies, some uncertainty remained about its behavior.

New insights into hydrogen bonding in hydrogen sulfide

Philipp Meyer and Svenja Jäger. Credit: Yvonne Kasper

High-resolution infrared spectroscopy in superfluid helium nanodroplets

The spectroscopic technique used to record H2S molecules is quite unconventional. To perform the experiment, a single molecule of H2S was embedded in a superfluid helium droplet in a vacuum chamber.

Bochum researchers Svenja Jäger, Philipp Meyer and Jai Khatri statistically controlled the number of molecules picked up by a helium droplet by varying the amount of H2S gas in the vacuum chamber, and found that on average two H2S We were able to optimize the conditions to obtain gas. Molecules are always picked up at the same time.

The droplets are made of superfluid helium, which retains some unique properties compared to regular fluids. Some of their special features are extremely high thermal conductivity that brings the droplet and its embedded molecules close to absolute zero Kelvin, transparency over the spectral range from ultraviolet to far infrared, and fluid-to-fluid interaction. There is almost no effect. Embedded molecules.

These three features are critical to the performance of the experiment, as they allow scientists to investigate the interactions between two H2S molecules without interference from other molecules or thermal energy.

This resulted in high-resolution IR spectra that displayed not only the vibrational motion of the H2S dimer but also its rotation and tunnel splitting. Tunnel splitting describes the separation of energy levels by a small energy barrier between two different structures of the same molecule.

Fundamentals for a deeper understanding of hydrogen bonding

These experimental results were complemented by theoretical calculations, making it possible to characterize the energy splitting of H2S molecules in the ground and excited states. Compared to water, we found that the bonds between H2S molecules are more flexible in the ground state. Still, when one of the molecules is excited, the hydrogen bonds become very similar to those in water.

In addition, researchers can further characterize and reassign vibrational signals already published by other chemists, presenting a sensitive test of state-of-the-art computational methods. These methods are used to predict the interactions of various molecules and to verify that the predictions are correct. Must be compared with experiment.

The study of the bonds between small molecules, such as water and in this case H2S, not only greatly increases our understanding of fundamental chemistry and supports the understanding of more complex chemical systems, but also enables the development of more accurate theoretical calculations. Masu.

Further information: Svenja Jäger et al, On the nature of hydrogen bonds in H2S dimers, Nature Communications (2024). DOI: 10.1038/s41467-024-53444-6

Provided by Ruhr University Bochum

Citation: High-resolution IR spectroscopy reveals new insights into hydrogen bonding in hydrogen sulfide (November 12, 2024) https://phys.org/news/2024-11-high-resolution-ir-spectroscopy – Retrieved on November 12, 2024 from reveal.html

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