The measured 10 μm refractive index of some simple molecules (CO, H2O, CH4, C2H2) and their calculated extension to the whole IR frequency region

The refractive index of some simple molecules has been determined with different CO2 laser lines in the 10 μm region. Some gases show a frequency dependence of the refractive index. This frequency behaviour can be related in a simple way to the presence of an absorption band adjacent to the 10 μm region. This simple relation allows to derive with good accuracy the integrated absorption intensity Sν0 of the involved bands. In this way the model validity is confirmed and the model can be used to calculate the theoretical refractivity over the whole IR region (<5000 cm−1) by using the Sν0 values of all the IR bands reported in literature.