Infrared electroabsorption spectroscopy
Development of novel spectroscopic techniques is quite important in natural sciences because it serves as a new tool to elucidate mechanisms and rules underlying natural phenomena. Fundamental properties of molecules like chemical bonding and reactivity are influenced profoundly by electrostatic interactions, and it is of importance to elucidate these interactions by observing the responses of molecules to an applied external electric field. Such kinds of experiments (Stark spectroscopy) have been performed extensively using UV-visible absorption and fluorescence spectra, whereas there were only few vibrational spectroscopic studies.
We have developed infrared electroabsorption spectroscopy by combining dispersive IR spectrometer and the AC coupled amplifier system, and succeeded in detecting the ΔA signal of 1,2-dichloroethane as small as 10-7 in 2001 . This is a novel technique that provides information not only on electronic properties of vibrationally excited states (as has been shown in the UV-visible region) but also on the electric field effect on the molecular structure . Using this apparatus, we have succeeded in detecting the IR electroabsorption signal of organic liquid molecules at room temperature and elucidated the responses of N-methylacetamide , liquid crystal (5CB) , and p-nitroaniline . The obtained spectra brought much inforamtion about the structure as well as the structural changes of each molecules in liquids with the electric field modulation.
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