Anomalous Bands in Infrared Difference Spectra Due to Frequency Shifts

Artifacts appearing in infrared difference spectra can be caused by the lack of wavelength reproducibility and/or molecular interactions such as solvent effects. These artifacts appear as derivatives in difference spectra. Experimental spectra containing a number of bands with a variety of bandwidths were shifted over a range of frequencies and subtracted from the original spectra to intentionally produce anomalous bands. Models based on both Lorentzian and Gaussian band shapes were used to fit the observed data, and it was found that either band shape could be used to adequately predict the observed results within the experimental error of the measurements. Moreover, the models can be used to determine the values of the frequency shifts from the peak-to-peak differences of artifacts.