"Sum-frequency spectroscopy as a novel probe of molecular chirality"
M. A. Belkin
UC Berkeley
Lawrence Berkeley National Laboratory
Wednesday, March 10, 2004 -11 AM -12 Noon in 375 LeConte Hall
Abstract
Molecular chirality plays an important role in chemistry, biology, and
medicine. Traditional optical techniques for probing chirality, such as circular dichroism
and Raman optical activity rely on electric-dipole forbidden transitions. As
a result, their intrinsic low sensitivity limits their use to proble bulk chirality
rather than chiral surfaces, monolayers or thin films often important for
chemical or biological systems. Contratry to the traditional chirality probes, chiral
signal in sum-frequency generation (SFG) is electric-dipole allowed both on chiral
surface and in chiral bulk making it a much more promising tool for probing molecular
chirality.
SFG from a chiral medium was first proposed in 1965, but was not confirmed
experimentally. Here we describe the set of experiments in our lab that successfully
demonstrate the effect . We also show that with tunable inputs SFG can be used
as a sensitive spectroscopic tool to probe chirality in electronic and
vibrational resonances of chiral molecules. We demonstrate monolayer sensitivity
for both vibrational and electronic SFG. We also discuss the revelvant theoretical
models explaining the origin and the strength of chiral signal in vibrational and
electronic SFG spectroscopies.
