Observation and calculation of vibrational circular birefringence: A new form of vibrational optical activity


  • Contribution to the Special Thematic Project “Advances in Chiroptical Methods”


We report the first mid-infrared observation of vibrational circular birefringence (VCB) arising from individual chiral molecules. VCB can also be called vibrational optical rotatory dispersion (VORD) and is the Kramers-Kronig transform of vibrational circular dichroism (VCD). The method of measurement involves a simple change in the optical set-up and electronic processing of a VCD spectrometer such that the VCB spectrum appears at twice the polarization modulation frequency as a pseudo vibrational linear dichroism (VLD) spectrum. VCB spectra are also calculated with density function theory (DFT) for the first time using a commercially available program for rotational strengths where the calculated intensities are convolved with the real, dispersive part of a normalized complex Lorentzian lineshape rather than the imaginary, absorptive part, normally used for IR and VCD intensity calculations. Comparison of themeasured and calculated VCB, VCD, and IR spectra of (+)-R-limonene and (−)-S-α-pinene show close agreement and confirm the validity of the new VCB measurements. Chirality 21:E277–E286, 2009. © 2009 Wiley-Liss, Inc.