2) A and D 2 significantly correlate to molecular symmetry. A symmetric molecule gives a much smaller A, and in most cases, D 2 =1 or 0.9999, whereas an asymmetric molecule gives an inverse. For example, cyclopropane is symmetric; thus, A=3.7396, D 2 =1. In contrast, propane is asymmetric; therefore, A=5.0709, D 2 =0.9974. As a result, A and D 2 may be the criteria for assessing the molecule's symmetry. 3) As shown in Fig. , in the cases of smaller D 2 , e.g., NF3: D 2 =0.999, the linear regression can proceed in different temperature intervals to gain D 2 →1 as possible. It is natural and rational because, for asymmetric molecules, the packing status of molecules in a liquid may be affected by the temperature. For example, as the temperature increases from M.P. to Tc, NF3: A decreases from 5.7103 to 3.6213, while B (absolute value) decreases from 1566.7 to 1317.8 K.