Diatomic gas

A gas whose constituent molecules have two atoms. In the classical ideal-gas regime with three translational and two rotational degrees of freedom active but vibration frozen, $c_v=5\mathcal{R}/2$, $c_p=7\mathcal{R}/2$ and $\gamma =7/5$. Vibrational excitation, rotational freezing or chemical changes alter this heat-capacity model.