VAPOR-PRESSURE OF PARTIALLY DEUTERATED METHANES (CH3D, CH2D2, AND CHD3)

The difference between the vapor pressure of completely protiated or d euterated methane (CH4 or CD4) and partially deuterated methanes (CH3D , CH2D2, or CHD3) has been measured over the 96-121 K temperature rang e. The vapor pressure data obtained were fitted to equations of the ty pe T ln(p/p')=A/T+B, where the prime always refers to the Lighter mole cule. Within the studied temperature range, the vapor pressure isotope effect was found to be ''inverse'' (p >p') for all the systems, excep t in the low-temperature range of the (CH4/CH3D) system. Our data agre es with other results found in the literature, both experimental and t heoretical. Differences in the enthalpy of vaporization were calculate d from the experimental results. In the case of the CH4/CHD3) system, our vapor pressure isotope effect (VPIE) results were also compared wi th liquid-vapor isotope fractionation factor (LVIFF) data from other a uthors. (C) 1997 American Institute of Physics.