Previous work has shown that very small spherical scatterers may exhibit “unconventional” Fano resonances. Above all, we evaluate whether these features can be accurately modeled with Fano theory and whether they can be corrected (i.e., related to a pure Lorentzian absorption line shape), and if so, to what extent and under what conditions. With this motivation, we evaluate whether observed spectral features may be interpreted as Fano resonances, where sharp resonating bands are coupled to a slowly varying background process. Absorbance spectra that contain such dispersion effects, however, also share these signature features and bear a striking resemblance to Fano line shapes. Gardner, “ The inherent problem of transflection-mode infrared spectroscopic microscopy and the ramifications for biomedical single point and imaging applications,” Analyst 138, 144– 157 (2013). Diem, “ Line shape distortion effects in infrared spectroscopy,” Analyst 137, 3954– 3964 (2012). which involves a distortion of the transmission spectrum due to reflectance line shapes. Gardner, “ Resonant Mie scattering in infrared spectroscopy of biological materials–understanding the ‘dispersion artefact,’” Analyst 134, 1586– 1593 (2009). Generally speaking, Fano resonances occur due to a coupling between multiple oscillators in many physical systems this can be interpreted as an interference between a resonance of interest and a “background process.”Īsymmetric, derivative-like peaks are often observed in FTIR transmission and absorbance spectra, attributed to the “dispersion artefact,” 12 12. Pucci, “ Importance of plasmonic scattering for an optimal enhancement of vibrational absorption in SEIRA with linear metallic antennas,” J. Altug, “ Engineered absorption enhancement and induced transparency in coupled molecular and plasmonic resonator systems,” Nano Lett. Maier, “ Fano resonances in nanoscale plasmonic systems: A parameter-free modeling approach,” Nano Lett. Kim, “ Classical analogy of Fano resonances,” Phys. it has since been shown to be a general interference phenomenon applicable to a wide range of classical and quantum resonating systems. Fano, “ Sullo spettro di assorbimento dei gas nobili presso il limite dello spettro d’arco,” Il Nuovo Cimento 12, 154– 161 (1935). While Fano theory was originally developed in the context of quantum spectroscopy, 7 7. Identification and correction of such distortions are critical for FTIR spectroscopy if one seeks a quantitative understanding of the sample under investigation. Gardner, “ Resonant Mie scattering (RMieS) correction of infrared spectra from highly scattering biological samples,” Analyst 135, 268– 277 (2010). In such cases, identification of chemical bands in a scattering sample may be deceptive as the distorted bands frequently suffer from a shift in the peak position. Wood, “ Mie-type scattering and non-Beer-Lambert absorption behavior of human cells in infrared microspectroscopy,” Biophys. Previously, it has been shown that these derivative features occur due to a nonlinear mixing between the absorbance and dispersive spectra on top of a smooth-varying broadband baseline. De Haseth, Fourier Transform Infrared Spectrometry, Chemical Analysis ( Wiley, 1986), Vol. Asymmetrically distorted spectral peaks are often encountered in FTIR absorbance spectra-particularly noticeable in the Amide-I band, where a derivative-like line shape may be observed.