Isotope effects on vapor pressure

Abstract

The vapor pressure isotope effect of pure liquid is examined, and the vapor pressure ratios of two different isotopes are calculated. Based on the significant structure theory of liquids, the molecular weight effect on vapor pressure is found in the series of $CH_4/CD_4$, $GeH_4/GeD_4$, $SiH_4/SiD_4$; zero-point energy effect is found in the system of $C_2H_2D_2$ trans/$C_2H_2D_2$ (cis); and the effect of inter-molecular potential difference is found in the $CH_3OH$ $CH_3OD$ system. A new technique of formulating the hindered rotational partition function is proposed. Some thermodynamic functions are calculated using this partition function and compared with the Pitzer``s calculation. Inclusion of the hindered rotational partition function in calculation gives good quantitative agreement with experimental values.