Benzene is probably the most studied compound in the history of organic chemistry. Whenever a new experimental technique or theoretical method is being developed most of the time it is tested on benzene. This molecule can also be considered the parent compound for most molecular crystals based on C-H...pi interactions, in particular acenes. Aim of the present proposal is to understand the effect of isotope and chemical substitution on the vibrational properties of benzene in the crystalline state, via the characterization of the thermal expansion in C6H6, C6D6 and the per-alogenated benzenes in the temperature range 10 to 400K.