The aim of the present proposal is to complete a systematic study on the effects of isotopic and chemical substitution on the thermal expansion and vibrational properties of benzene. In the first experiment (RB 1720468) we had time to study C6H6, C6D6 and C6F6 in detail, and C6Br6 up to T/Tmelt = 0.6. We would like now to complete the study of the remaining hexa-halogenated benzenes. Preliminary results indicate that H- and D-benzene behave quite similarly, while C6F6 exhibits very large anisotropic thermal expansion. C6Br6 seems to show a more regular thermal expansion up to 60% of its melting point, but it would be useful to follow the volume expansion curve much closer to the melting point to characterise phenomena similar to those observed in C6F6. Both C6Cl6 and C6I6 have the same structure type of C6Br6 and will offer additional insight into the pi-halogen interaction.