Theoretical estimation of vapor pressure isotope effects
ZHANG Ji-xi;LIU Yun;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry, Chinese Academy of Sciences;University of Chinese Academy of Sciences;
The vapor pressure isotope effects(VPIE) has important applications in geosciences and cosmochemistry. Because different isotopologues have different saturated vapor pressures, the light isotopologues usually volatilize faster than heavy ones during volatilization processes, resulting in isotopic fractionations between the condensed phase and the gaseous phase. There is a direct connection between the VPIE and the isotope fractionation factor α. If we can obtain the VPIE of any compound, we can also obtain its isotope fractionation factor α between its condensed phase and gaseous phase. Using the method suggested by Bigeleisen, we show how to calculate the VPIE through calculating reduced partition function ratio(RPFR) of different isotopologues. Bigeleisen simplified such calculation into a way that only the harmonic frequencies of two isotopologues in condensed and gas phases are needed. In this study, we briefly review the calculation methods of VPIE and its general applications. We also use volatilization processes of water molecule and CdS as examples to show how to theoretically estimate VPIE.