TIFR
Department of Chemical Sciences
School of Natural Sciences

November 30, 2015 at 4.00 pm in AG-69

Title :

Ultrafast Vibrational Sum-Frequency Spectroscopy and Dynamics at Mineral/Aqueous Interfaces


Abstract :


The properties of water at interfaces are important in many disciplines. However, it is not clear what effects the presence of the surface, the charge that can develop on the surface, the solution ionic strength, and the interfacial electric field, have on how interfacial water molecules communicate with each other, e.g., how thermal (vibrational) energy flows. To address these issues we investigated the ultrafast vibrational population and dephasing dynamics of the O-H stretch using IR pump-vibrational Sum Frequency Generation (vSFG) probe at the water/mineral interfaces.[1] Contrary to previous reports, the vibrational lifetime of the O-H stretch at the silica/water interface is ~ 600 fs, a factor 2-3 slower than bulk water, when the surface is neutral.[1] Charging the SiO 2 interface appears to lead to a dramatic acceleration of vibrational relaxation. Experiments on the effect of ionic strength, suggest that the primary reason for accelerated dynamics at pH=6

is the sampling of water within the Debye length that has bulk-like solvation.[1] The pH dependent structuring of interfacial water and the influence of electrolyte also impact interfacial reactivity.[2]

 

A newly developed SFG spectrometer, based on a novel ultrabroadband optical parametric amplifier generating IR pulses in the ~2800-6000 cm -1 range bandwidths >2000 cm -1 in the near-IR range, allows vSFG spectroscopy, including low-intensity features such as non-hydrogen bonded OH vibrations and combination [stretch+bend] and overtone bands of interfacial water.[3] Access to these modes opens up opportunities for investigations of a broad range of interfaces.

 

  1. The Effect of Electric Fields on the Ultrafast Vibrational Relaxation of Water at a Charged Solid-LiquidInterface as Probed by Vibrational Sum Frequency Generation, A. Eftekhari-Bafrooei and E. Borguet, J.Phys. Chem. Lett.,, 2, 1353-1358 (2011)

 

  1. Experimental Correlation Between Interfacial Water Structure and Mineral Reactivity. Dewan, S.;Yeganeh, M. S.; Borguet, E., J. Phys. Chem. Lett., 2013, 4 (11), 1977-1982.

 

  1. Observation of the Bending Mode of Interfacial Water at Silica Surfaces by Near Infrared VibrationalSum-Frequency Generation Spectroscopy of the [stretch+bend] Combination Bands. Oleksandr Isaienko, Satoshi Nihonyanagi, Devika Sil, and Eric Borguet, J. Phys. Chem. Lett., 4, 531-535, (2013)