[MOS] April 10, 2007

[Zina Queen]

Seminar on
Modern Optics and Spectroscopy


Andrei Tokmakoff, MIT

The fluctuations and switching of hydrogen bonds in water

April 10, 2007

12:00 - 1:00 p.m.
Grier Room 34-401



Ultrafast infrared spectroscopy of the OH stretching vibration of HOD 
in D2O can be used to resolve the structural rearrangements of 
water's hydrogen bonding network. Infrared spectroscopy of the OH 
stretch is an ideal technique because of its sensitivity to hydrogen 
bonding configurations. Conceptually our experiments aim to correlate 
the OH stretch frequency with the hydrogen bonded environment and 
then watch the time dependence of this frequency in order to report 
on the exchange of hydrogen bonding structures. Our studies reveal 
the vibrations and hindered rotational fluctuations of individual 
hydrogen bonds in water prior to a reconfiguration of the many-body 
liquid structure on picosecond time scales. Additionally, 
two-dimensional infrared spectroscopy of this transition provides 
information on the mechanism of hydrogen bond rearrangements. Our 
experimental results indicate that hydrogen bond switching is a 
concerted process in which a ruptured hydrogen bond appears only 
fleetingly as a transition state along the hydrogen bond switching 
coordinate.
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