Theoretical and calculational aspects of the radio refractive index of water vapor

The radio refractive index is calculated by summing the refraction due to the infrared resonances of the water vapor monomer. Although this calculated refraction agrees well with measured values, its temperature dependence departs significantly from the measured variation with temperature. The rotational resonances of water vapor give a contribution to the radio refractive index that does not vary precisely as e/T 2 ; theoretical reasons are given for this departure from the classical refraction by permanent dipoles.