Modeling index of refraction of dilute gases

[Habeebe]

I'm interested in predicting the index of refraction of atmospheric air and several nonpolar gases at room temperature for pressures of 1 atm - 0 atm. I'm not really sure where to get started. I have found the relation $$n=\sqrt{1+\frac{3AP}{RT}}$$ but I don't really get where it comes from. Well, it was said to come from the Lorentz-Lorenz equation, but the Lorentz-Lorenz equation describes crystals so I have no clue how you turn it into a description of gases.

Basically, I need to find a way to draw a curve predicting index of refraction as a function of pressure over the 0-1 atm range for various gases, and I don't know how to figure out what the dependence is.

 

[M Quack]

This paper and the reference 7 cited give an introduction to the topic.

http://web.mit.edu/ytc/www/HLMA/Ref/opticsPaper02.pdf