Vibrational circular dichroism spectroscopy of solid polymer films: effects of sample orientation

Vibrational circular dichroism (VCD) spectra of anisotropic thin solid samples are often superimposed with large contributions of linear birefringence and linear dichroism. In this study a theoretical approach is given on how to extract the true VCD spectrum out of such superimposed spectra. To verify this approach, the VCD spectra of achiral polymer films were examined. The polymers are supposed to give a zero line as VCD spectrum after eliminating the linear contributions. Applying our approach, in which four VCD spectra in different but selected sample orientations are recorded, and calculating their average, leads to the expected result, i.e., a zero line for achiral polymers. The advantage of this method for the elimination of artifacts from solid-state VCD spectra is that no further measurements are required (e.g., linear dichroism measurements or the determination of the orientation with the maximum anisotropy).