that (classically) rises from 
at low temperature, to 
at moderate temperature (due to the excitation of the rotational degrees of freedom), to 
at high temperature (due to the excitation of vibrations). [P7.4]
is: an ideal gas in which the internal energy is a function of temperature that (classically) rises from at low temperature, to at moderate temperature (due to the excitation of the rotational degrees of freedom), to at high temperature (due to the excitation of vibrations). [P7.4]
can be used: to model the behaviour of a real gas with two atoms per molecule at low density. [P7.4]
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