For gases whose molecules are not spherically symmetric, the expression formula_91 still holds. In contrast with spherically symmetric molecules, however, formula_84 varies significantly depending on the particular form of the interparticle interactions: this is a result of the energy exchanges between the internal and translational degrees of freedom of the molecules. An explicit treatment of this effect is difficult in the Chapman–Enskog approach. Alternately, the approximate expression formula_93 was suggested by Eucken, where formula_94 is the heat capacity ratio of the gas.