Dynamical Collectivity and Nuclear Quantum Effects on the Intermolecular Stretching Mode of Liquid Water

• Published in: The journal of physical chemistry. B Vol. 125; no. 6; pp. 1632 - 1639
• Main Authors: Shiraga, Keiichiro, Fujii, Yasuhiro, Koreeda, Akitoshi, Tanaka, Koichiro, Arikawa, Takashi, Ogawa, Yuichi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18.02.2021
• Subjects: B: Liquids; Chemical and Dynamical Processes in Solution
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/acs.jpcb.0c10154

This study investigated the broadband terahertz and low-frequency Raman spectroscopy of liquid water (H2O, D2O, and H2 18O) over 2 decades of frequency to address long-standing challenges regarding the interpretation of the intermolecular stretching mode at around 5 THz. We experimentally demonstrated that the intermolecular stretching mode of liquid water obtained via terahertz spectroscopy is significantly redshifted and broadened compared with that via Raman. This result was rationalized by the enhanced dynamical collectivity probed by terahertz spectroscopy, although both have a common origin in the kinetic motion. Their temperature and isotope dependences emphasize the significance of oscillation mass in determining the intermolecular stretching lineshape, while quantum effects cannot be overlooked in both terahertz and low-frequency Raman spectra.