Hydrogen and Carbon Vapour Pressure Isotope Effects in Liquid Fluoroform Studied by Density Functional Theory

H/D and C-12/C-13 vapour pressure isotope effects (VPIEs) in liquid fluoroform (CHF3) were studied at the MPW1PW91/6-31 ++ G(d) level of theory. The CHF3 monomer and CHF3 molecules surrounded by other CHF 3 molecules in every direction in CHF3 clusters were used as model molecules of vapour and liquid CHF3. Although experimental results in which the vapour pressure of liquid (CHF3)-C-12 is higher than that of liquid (CDF3)-C-12 and the vapour pressure of liquid (CHF3)-C-13 is higher than that of liquid (CHF3)-C-12 between 125 and 212 K were qualitatively reproduced, the present calculations overestimated the H/D VPIE and underestimated the C-12/C-13 VPIE. Temperaturedependent intermolecular interactions between hydrogen and fluorine atoms of neighbouring molecules were required to explain the temperature dependences of both H/D and C-12/C-13 VPIEs.