稳定同位素交换反应平衡常数与平衡分馏因子的关系——过量因子的实质及计算方法  

The Relationship Between the Equilibrium Constant and Fractionation Factors in Isotope Exchange Reactions: the Role of the Excess Factor and Its Calculation Method

作　　者：张继习[1] 刘耘[1] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550002

出　　处：《矿物学报》2011年第1期126-132,共7页Acta Mineralogica Sinica

基　　金：国家自然科学基金(批准号:4077300541073015);矿床地球化学国家重点实验室专项经费

摘　　要：理论计算稳定同位素平衡分馏因子(α),是以计算平衡常数K为桥梁,但是K与α之间并非简单的指数关系,二者之间还存在一个较为神秘的过量因子X(excess factor)。然而,几乎所有的理论计算工作都直接忽略了过量因子,并没有人详细研究过过量因子的实质及其可以被忽略的条件,因此,针对这个现状,本文从最基础的理论推导开始,精确推导了α和K之间的关系,并得到了过量因子的具体表达式,同时也给出了β因子(一种物质与其理想气态原子之间的平衡分馏因子)和同位素约化配分函数比(RPFR)之间的具体关系式。本文还以石膏与溶液中硫酸根之间的硫和氧同位素的分馏为实例,具体展示了过量因子产生的原因和计算方法,也提供了精确的石膏和硫酸根之间的硫和氧同位素的平衡分馏参数。Theoretically,the fractionation factor（α） is calculated based on the calculation of equilibrium constant K.However,the relationship between K and α is not simply follow the power-law rule.There is a so-called excess factor in between.Unfortunately,almost all previous studies ignored the excess factor.This study deduced out the precise equation for the excess factor and the relationship between K and α.Consequently,we also obtain the relationship between excess factor,β factor and the reduced partition function ratio（RPFR）.For illustrating the excess factor and its calculation procedure,the isotope fractionation of gypsum vs.sulfate was used as an example.Precise equilibrium fractionation factors of O and S isotopes of gypsum and sulfate were also obtained.

关 键 词：平衡分馏因子 平衡常数 过量因子 β因子 Bigeleisen-Mayer公式 石膏-硫酸根分馏 

分 类 号：P597[天文地球—地球化学]