title: Water vibrations have strongly mixed intra- and intermolecular character.
abstract: The ability of liquid water to dissipate energy efficiently through ultrafast vibrational relaxation plays a key role in the stabilization of reactive intermediates and the outcome of aqueous chemical reactions. The vibrational couplings that govern energy relaxation in H2O remain difficult to characterize because of the limitations of current methods to visualize inter- and intramolecular motions simultaneously. Using a new sub-70 fs broadband mid-infrared source, we performed two-dimensional infrared, transient absorption and polarization anisotropy spectroscopy of H2O by exciting the OH stretching transition and characterizing the response from 1,350 cm(-1) to 4,000 cm(-1). These spectra reveal vibrational transitions at all frequencies simultaneous to the excitation, including pronounced cross-peaks to the bend vibration and a continuum of induced absorptions to combination bands that are not present in linear spectra. These observations provide evidence for strong mixing of inter- and intramolecular vibrations in liquid H2O, and illustrate the shortcomings of traditional relaxation models.
authors.affiliation: 1] Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA [2] [3].
authors.forename: Krupa
authors.initials: K
authors.lastname: Ramasesha
authors.forename: Luigi
authors.initials: L
authors.lastname: De Marco
authors.forename: Aritra
authors.initials: A
authors.lastname: Mandal
authors.forename: Andrei
authors.initials: A
authors.lastname: Tokmakoff
mesh_terms: D006860:Hydrogen Bonding; D008958:Models, Molecular; D013816:Thermodynamics; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water