biostudies-literatureZhang YNational Science Foundatione2020941118https://www.ebi.ac.uk/biostudies/studies/S-EPMC8501843biostudies-literatureUnknown118(40)Because of their central importance in chemistry and biology, water molecules have been the subject of decades of intense spectroscopic investigations. Rotational spectroscopy of water vapor has yielded detailed information about the structure and dynamics of isolated water molecules, as well as water dimers and clusters. Nonlinear rotational spectroscopy in the terahertz regime has been developed recently to investigate the rotational dynamics of linear and symmetric-top molecules whose rotational energy levels are regularly spaced. However, it has not been applied to water or other lower-symmetry molecules with irregularly spaced levels. We report the use of recently developed two-dimensional (2D) terahertz rotational spectroscopy to observe high-order rotational coherences and correlatiProceedings of the National Academy of Sciences of the United States of AmericaNonlinear rotational spectroscopy reveals many-body interactions in water molecules.PMC8501843CHE-1665383Li XField RWCoy SLNelson KAZhang YShi JfalseNonlinear rotational spectroscopy reveals many-body interactions in water molecules.Because of their central importance in chemistry and biology, water molecules have been the subject of decades of intense spectroscopic investigations. Rotational spectroscopy of water vapor has yielded detailed information about the structure and dynamics of isolated water molecules, as well as water dimers and clusters. Nonlinear rotational spectroscopy in the terahertz regime has been developed recently to investigate the rotational dynamics of linear and symmetric-top molecules whose rotational energy levels are regularly spaced. However, it has not been applied to water or other lower-symmetry molecules with irregularly spaced levels. We report the use of recently developed two-dimensional (2D) terahertz rotational spectroscopy to observe high-order rotational coherences and correlati2021-01-01T00:00:00Z2021 Oct2025-04-19T18:17:29.327Z2025-04-19T18:17:29.327ZS-EPMC85018433458830110.1073/pnas.2020941118