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 is othermal and isobaric conditions from the liquid to the supercritical domai n using neutron diffraction and molecular dynamics simulation. The short-ra nge local ordering existing at ambient conditions involving dimers in which the molecules are in a parallel stacked configuration, is progressively we akened at the isobaric condition (P = 16 MPa) upon increasing the temperatu re up to 573 K. Under isothermal conditions (573 K) and as the density goes down to about rho(r) = rho/rho(c) = 0.43 (reduced density), although the o rientational ordering reaches in the fluid a more random distribution, dime rs are still present (two thirds of the proportion estimated at ambient con ditions). (C) 2000 Published by Elsevier Science B.V.