Structural study of the 1-3-5 trifluorobenzene dimer stability: from liquid to gas densities using supercritical conditions

The local ordering in 1,3,5-trifluorobenzene has been investigated under isothermal and isobaric conditions from the liquid to the supercritical domain using neutron diffraction and molecular dynamics simulation. The short-range local ordering existing at ambient conditions involving dimers in which the molecules are in a parallel stacked configuration, is progressively weakened at the isobaric condition (P=16 MPa) upon increasing the temperature up to 573 K. Under isothermal conditions (573 K) and as the density goes down to about ρr=ρ/ρc=0.43 (reduced density), although the orientational ordering reaches in the fluid a more random distribution, dimers are still present (two thirds of the proportion estimated at ambient conditions).