A formula for the refractive index of a gas dependent on temperature and pressure

I am in search for a formula that gives me the refractive index of a gas at a given temperature and pressure. Does such a formula exist? Ideally the solution should have this form:

$$n_g(t, p) = \ldots$$,

where $$n_g$$ is the refractive index of the gas $$g$$, $$t$$ is the temperature and $$p$$ is the pressure.

• n(g)-1=k* density, the k factor is called Gladstone-Dale coefficient. You can always look up gas density in the literature tables. books.google.com/… – M. Farooq Apr 26 '19 at 12:41