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.

SUBMITTER: van der Post ST 

PROVIDER: S-EPMC4595750 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature