H/D and 12C/13C 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 CHF3 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 12CHF3 is higher than that of liquid 12CDF3 and the vapour pressure of liquid 13CHF3 is higher than that of liquid 12CHF3 between 125 and 212 K were qualitatively reproduced, the present calculations overestimated the H/D VPIE and underestimated the 12C/13C VPIE. Temperature-dependent intermolecular interactions between hydrogen and fluorine atoms of neighbouring molecules were required to explain the temperature dependences of both H/D and 12C/13C VPIEs.

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