title: Strong frequency dependence of vibrational relaxation in bulk and surface water reveals sub-picosecond structural heterogeneity.
abstract: Because of strong hydrogen bonding in liquid water, intermolecular interactions between water molecules are highly delocalized. Previous two-dimensional infrared spectroscopy experiments have indicated that this delocalization smears out the structural heterogeneity of neat H2O. Here we report on a systematic investigation of the ultrafast vibrational relaxation of bulk and interfacial water using time-resolved infrared and sum-frequency generation spectroscopies. These experiments reveal a remarkably strong dependence of the vibrational relaxation time on the frequency of the OH stretching vibration of liquid water in the bulk and at the air/water interface. For bulk water, the vibrational relaxation time increases continuously from 250 to 550 fs when the frequency is increased from 3,100 to 3,700 cm(-1). For hydrogen-bonded water at the air/water interface, the frequency dependence is even stronger. These results directly demonstrate that liquid water possesses substantial structural heterogeneity, both in the bulk and at the surface.
authors.affiliation: FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Sietse T
authors.initials: ST
authors.lastname: van der Post
authors.affiliation: FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.|Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Cho-Shuen
authors.initials: CS
authors.lastname: Hsieh
authors.affiliation: Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Masanari
authors.initials: M
authors.lastname: Okuno
authors.affiliation: Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nagata
authors.affiliation: FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Huib J
authors.initials: HJ
authors.lastname: Bakker
authors.affiliation: Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn
authors.affiliation: Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Hunger