The interaction of chiral molecules and light shows different absorption for both enantiomers depending on the circular polarization of light. The absorption of right circularly polarized light AR and left circularly polarized light AL for optically active compounds is of different intensity. The difference ΔA = AL-AR is unequal to zero for all chiral molecules. This effect is known as circular dichroism.
In contrast the difference ΔA = AL-AR for all nonchiral compounds, e.g. racemic mixtures or isotropic molecules is zero which means the optical activity is lifted and no optical activity is present respectively.
In general VCD signals are recorded in transmission and the intensities range between 10-4 and 10-5 absorption units typically. From that point of view it is convincing that highest performance is needed with respect to the FTIR spectrometer in order to obtain the necessary sensitivity. For that purpose Bruker offers the PMA 50. Combined with Bruker’s INVENIO and VERTEX FTIR spectrometers an unmatched powerful and flexible system is formed.