Observation of the Low-Frequency Spectrum of the Water Trimer as a Sensitive Test of the Water-Trimer Potential and the Dipole-Moment Surface

© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. Intermolecular interactions in bulk water are dominated by pairwise and non-pairwise cooperative interactions. While accurate descriptions of the pairwise interactions are available and can be tested by precise low-frequency spectra of the water dimer up to 550 cm−1, the same does not hold for the three-body interactions. Here, we report the first comprehensive spectrum of the water trimer in the frequency region from 70 to 620 cm−1 using helium-nanodroplet isolation and free-electron lasers. By comparison to accompanying high-level quantum calculations, the experimentally observed intermolecular bands can be assigned. The transition frequencies of the degenerate translation, the degenerate in-plane and the non-degenerate out-of-plane libration, as well as additional bands of the out-of-plane librational mode are reported for the first time. These provide a benchmark for state-of-the-art water potentials and dipole-moment surfaces, especially with respect to three-body interactions

Investigation of small water clusters using helium nanodroplet isolation spectroscopy

Die vorliegende Arbeit behandelt die infrarotspektroskopische Untersuchung kleiner Wassercluster, welche in Heliumnanotröpfchen isoliert wurden. Im Rahmen dieser Arbeit wurden Untersuchungen der intramolekularen Biegeschwingungen sowie der intermolekularen Moden kleiner Wassercluster, insbesondere des Wasser-Dimers und Wasser-Trimers, durchgeführt. Für die intermolekularen Moden wurden spektrale Aufspaltungen beobachtet, welche durch charakteristische Tunnelbewegungen der Wassercluster erklärt werden konnten. Dazu erfolgte eine gruppentheoretische Beschreibung der Tunnelbewegungen. Basierend auf den experimentellen Spektren konnte der Einfluss der Vibrations-Anregung auf die Tunnelbewegungen abgeschätzt werden

Observation of the Low-Frequency Spectrum of the Water Dimer as a Sensitive Test of the Water Dimer Potential and Dipole Moment Surfaces

Contains fulltext : 206886.pdf (publisher's version ) (Closed access)9 p

Observation of the Low‐Frequency Spectrum of the Water Trimer as a Sensitive Test of the Water‐Trimer Potential and the Dipole‐Moment Surface

© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. Intermolecular interactions in bulk water are dominated by pairwise and non-pairwise cooperative interactions. While accurate descriptions of the pairwise interactions are available and can be tested by precise low-frequency spectra of the water dimer up to 550 cm−1, the same does not hold for the three-body interactions. Here, we report the first comprehensive spectrum of the water trimer in the frequency region from 70 to 620 cm−1 using helium-nanodroplet isolation and free-electron lasers. By comparison to accompanying high-level quantum calculations, the experimentally observed intermolecular bands can be assigned. The transition frequencies of the degenerate translation, the degenerate in-plane and the non-degenerate out-of-plane libration, as well as additional bands of the out-of-plane librational mode are reported for the first time. These provide a benchmark for state-of-the-art water potentials and dipole-moment surfaces, especially with respect to three-body interactions

Acid solvation versus dissociation at "stardust conditions": Reaction sequence matters

Contains fulltext : 206118.pdf (publisher's version ) (Open Access)8 p

Observation of the low-frequency spectrum of the water dimer as a sensitive test of the water dimer potential and dipole moment surfaces

Using the helium nanodroplet isolation setup at the ultrabright free‐electron laser source FELIX in Nijmegen (BoHeNDI@FELIX), the intermolecular modes of water dimer in the frequency region from 70 to 550 cm$^{−1}$ were recorded. Observed bands were assigned to donor torsion, acceptor wag, acceptor twist, intermolecular stretch, donor torsion overtone, and in‐plane and out‐of‐plane librational modes. This experimental data set provides a sensitive test for state‐of‐the‐art water potentials and dipole moment surfaces. Theoretical calculations of the IR spectrum are presented using high‐level quantum and approximate quasiclassical molecular dynamics approaches. These calculations use the full‐dimensional ab initio WHHB potential and dipole moment surfaces. Based on the experimental data, a considerable increase of the acceptor switch and a bifurcation tunneling splitting in the librational mode is deduced, which is a consequence of the effective decrease in the tunneling barrier