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Consequences of chirality in second-order non-linear spectroscopy at surfaces
J M Hicks1, T Petralli-Mallow, J D Byers
1Department of Chemistry, Georgetown University, Washington DC 20057, USA.
Faraday Discussions
|January 1, 1994
Summary
Surface second-harmonic generation (SHG) detects chiral molecules using polarized light. This new spectroscopic method offers enhanced sensitivity for studying chiral surfaces, surpassing traditional circular dichroism (CD) methods.
Area of Science:
- Non-linear optics
- Surface science
- Chiroptical spectroscopy
Background:
- Surface second-harmonic generation (SHG) is a surface-sensitive nonlinear spectroscopic technique.
- Circular dichroism (CD) spectroscopy is a standard method for studying chiral molecules.
- Existing methods lack sufficient sensitivity for certain chiral surface analyses.
Purpose of the Study:
- To develop a new optical method for studying chiral surfaces.
- To investigate the detection of dichroic behavior in SHG analogous to CD spectroscopy.
- To explore the potential of SHG for chiral molecular analysis.
Main Methods:
- Utilized surface second-harmonic generation (SHG) spectroscopy.
- Employed left- and right-handed circularly polarized excitation beams.
- Studied oriented monolayers of chiral molecules (R)- and (S)-2,2'-dihydroxy-1,1'-binaphthyl (BN).
Main Results:
- Observed strong dependence of SHG efficiency on the polarization of the excitation beam.
- Demonstrated significantly larger differential SHG signals compared to conventional CD spectroscopy.
- Attributed large chiroptical effects to the chiral element chi(xyz) of the second-order nonlinear tensor chi(2).
Conclusions:
- Developed a novel chiral spectroscopy based on SHG.
- Showcased SHG's capability to measure chiral properties of adsorbed molecules with high sensitivity.
- Established SHG as a powerful tool for chiral surface analysis, distinct from linear spectroscopies.