Figure , Curves of Y ~1/T and the results of linear regression of some representative gases Figure summarizes the average A values of small molecules. It is striking that some asymmetric molecules, e.g., CO, exhibit better symmetry than those symmetric molecules, for instance, CO2, under the theory of mass symmetry. It supports the suggestion of molecular orbital symmetry. Fig. shows the average A values of hydrocarbon molecules. Four linear relationships are observed. For example, except for CH4, the straight-chain alkanes with an even number of carbons and those with an odd number of carbons stand on a straight line, respectively. It reflects the better symmetry of alkanes with an even number of carbons. However, cyclo-C4F8 does not fall on the line composed of CH4, cyclopropane, etc. Combining the higher A values of fully fluorinated alkanes indicates that the effects of unbonded p orbitals of Fluorine are significant. A striking observation is that the A value of propene equals that of propane, while the spot of benzene overlaps that of cyclohexane. It is beyond the anticipation provoked by the symmetry of a double bond. 𝑅 is the entropy change of evaporation (ΔSv), A must be an item reflecting the entropic contribution of symmetry operations because the item of long-distance kinetic energy is set to 3/2. Moreover, the conventional mass symmetry is not suitable for describing the variations of A and D 2 . Therefore, the shapes of atomic/molecular orbitals are worthy of discussion.