Vapor pressure isotope effects in liquid fluoroform

The vapor pressures of isotopic fluoroforms 12CHF3, 13CHF3, and 12CDF3 have been measured at temperatures between 125 and 212 K in a modified Bigeleisen–Brooks–Ishida–Ribnikar cryostat. At all temperatures of measurement P(12CHF3)≳(12CDF3) and P(12CHF3)fluoroform molecules due to a kinetic energy coupling between the stretching motion and the molecular translation in the direction of the molecular figure axis, caused in large part by a weak but directional coulombic interaction between hydrogen and fluorine atoms of neighbor molecules.