Two types of theoretical models for an absorption band are described and applied to infrared absorption bands of CO2 and H2O. For CO2 , which has a regular fine structure, the so-called Elsasser model, which assumes equally-spaced, equally-intense lines, can be applied. For H2O, which has a highly irregular fine structure, the so-called statistical or Goody model, which assumes random spacings and intensity distribution, is applicable. The individual lines are assumed to have the Lorentz shape in both models. The method of application of these models to the experimentally observed bands is discussed in detail.
