In some IR spectra appearing in research articles, the bands have their base at the bottom of the graph and the peaks at the top (like stalagmites); however, in other spectra the bands appear "inverted" (stalactites). Only one of the following is an acceptable explanation.(A). "Inverted" spectra have negative absorbances because the absorptivity coefficient of the species of which the spectrum is recorded is negative(B). It depends on the optical configuration of the instrument: in some equipment the monochromator is between the source and the sample and in others between the sample and the detector(C). Some spectra are transmittance and others are absorbance(D). Everything depends on the number of lenses in the equipment's optics; if this number is odd, the spectrum comes out inverted