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

• Authors: Raffael Schwan, Ruhr University Bochum; Chen Qu, University of Maryland; Devendra Mani, Ruhr University Bochum; Nitish Pal, Ruhr University Bochum; Gerhard Schwaab, Ruhr University Bochum; Joel Bowman, Emory University; Gregory S. Tschumper, University of Mississippi; Martina Havenith, Ruhr University Bochum
• Journal Title: Angewandte Chemie (International Edition in English)
• Volume: Volume 59, Number 28
• Publisher: Wiley | 2020-05-28, Pages 11399-11407
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1002/anie.202003851
• Subjects: Chemistry, Biochemistry; Health Sciences, Radiology; Engineering, Biomedical
• Keywords: Science & Technology; Physical Sciences; Chemistry, Multidisciplinary; Chemistry; helium nanodroplets; vibrational spectroscopy; water cluster; water potential; Rotation tunneling spectroscopy; Infrared predisposition; Terahertz laser spectroscopy; Energy surface; Ab-inito; Quantitative characterization; Torsional manifold; VRT spectroscopy; Dimer

Abstract

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.