Characteristics of IR Spectrum

 

The ordinate (Y-axis) represents percent transmittance whereas the abscissa (X-axis) is either wavenumber or wavelength. It means that is the positions of IR absorption signals are presented as either wavenumbers or wavelengths (l). The wavenumber unit (in cm-1), reciprocal centimetre or centimetre inverse) however is  preferred over wavelength (in μm, micrometers), because an increase in it corresponds to an increase in energy (and frequency) whereas the wavelength is related inversely to the energy. Also, though abscissa is marked in cm_1 it is commonly (though incorrectly) referred to as the frequency. The frequency by itself is normally not used The infrared spectrum of a  compound consists of strong fundamental absorptions and weak overtones, combination band and Fermi resonance bands