Definition of Absorption Spectrum
The absorption spectrum is a plot on which the percent transmittance or absorption is measured as a function of frequency. This is plotted in the case of infrared and ultraviolet-visible spectroscopy. It can also be defined as the fraction of incident radiation that is being absorbed by the material over a range of frequencies. The atomic as well as the molecular composition of the material is used in the determination of the absorption spectrum.
The radiation is best absorbed by the material when it gets matched to the difference of energy between two quantum mechanical states of the sample molecule. The spectrum formed is composed of a number of lines. The width and shape of the lines give information about the spectral densities of the system.