Knowledge Bank

A modified design for a Fourier Transform Vibrational Circular Dichroism (FTIR-VCD) $spectrometer1$ based on a Nicolet Magna-IR 550 will be described. An external VCD bench incorporating lenses, polarizer, photoelastic modulator (PEM) and detector has been constructed. A ZnSe lens focuses the external collimated beam from the interferometer at the PEM. A KRS-5 linear polarizer and an optical filter are placed between the lens and the PEM. The beam emerging from the sample, which is placed immediately after PEM, is focused by another ZnSe lens on a liquid nitrogen cooled MCT $detector2,3$. The complete replacement of mirrors used in previous $versions4$ with lenses on the VCD bench enables us to obtain VCD spectra with high signal-to-noise ratio, minimized polarization artifacts and flat baselines. Single enantiomer VCD spectra can be collected routinely in about 15 minutes. Examples are presented illustrating the high performance characteristics of the instrument. Such a VCD bench could be adapted to many commercial FTIR spectrometers.