Structure of liquid carbon tetrachloride up to the subcritical point measured by wide Q-range neutron diffraction

Structure of liquid and gaseous CCl4 at elevated temperatures from 195 degrees C to the subcritical point 275 degrees C (T-c=285.15 degrees C) along the liquid-vapor coexistence curve have been studied by means of pulsed neutron diffraction. Structure factor in a wide range of momentum transfer Q from 0.03 to 20 Angstrom(-1), covering from the small angle scattering region to atomic-scale structure region, has been obtained. Long-range density fluctuation and atomic scale structure have been analyzed: (1) molecular orientational correlation still exists in Liquid CCl4 at 275 degrees C while it disappears in its saturated vapor; (2) correlation lengths of density fluctuation are 10-13 A for the liquid at 275 CC and 13-17 Angstrom for its saturated vapor: and (3) molecular-density fluctuation ([N-m(2)]-[N-m](2))/[N-m] is estimated to be 2.4 for the liquid at 275 degrees C and 9.3 for its saturated vapor. (C) 1997 American Institute of Physics.