EFFECT OF DEUTERIUM SUBSTITUTION ON THE VAPOR-PRESSURE OF DICHLOROMETHANE

The vapour pressure difference between CH2Cl2 and CD2Cl2 was measured by differential capacitance manometry between -40 and +40°C. The results can be expressed by the equation ln( pH Pa) = -(5.5133 ± 0.0047)/T (K). The vapour pressure of CH2Cl2 between -65 and +40°C has also been determined and the experimental data can be described by the Antoine equation log( pH Pa) = 9.1660-1122.5/(229.98 + t(°C)). The experimentally observed H/D vapour pressure isotope effect was interpreted within the framework of the statistical mechanical theory of condensed phase isotope effects. The results indicate that the rotation of the molecules about the axis parallel to the line joining the two chlorine atoms can be considered quasi free. © 1990.