稳定同位素分馏蒸汽压效应的计算方法  

Theoretical estimation of vapor pressure isotope effects

作　　者：张继习[1,2] 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 [2]中国科学院大学,北京100049

出　　处：《地球化学》2014年第1期1-10,共10页Geochimica

基　　金：国家自然科学基金(41073015;41173023)

摘　　要：稳定同位素分馏的蒸汽压效应(vapor pressure isotope effects,简称VPIE),在地球化学和天体化学上有着非常重要的研究意义。大部分情况下,由于轻重同位素体具有不同的蒸汽压,在经历挥发和蒸发过程时,含有重同位素的物种挥发得慢,轻同位素物种挥发得快,最终结果导致凝聚相富集重同位素,气相含有较多的轻同位素。在地球化学上,VPIE直接同非常重要的地学参数——同位素平衡分馏系数α联系在一起。本文应用Bigeleisen提出的方法,直接将VPIE和约化配分函数比(RPFR)相联系,只需要通过理论计算获得两种物质的简谐振动频率,就能够得到非高压情况下该物质的VPIE。本文以水和硫镉矿(CdS)为例,详细介绍了如何计算蒸发和气化过程VPIE的方法,并指出了其在天体化学和矿床学中的一些潜在应用。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 a. If we can obtain the VPIE of any compound, we can also obtain its isotope fractionation factor a 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 VP1E.

关 键 词：VPIE Bigeleisen—Mayer公式 同位素平衡分馏系数a RPFR 挥发 

分 类 号：P597[天文地球—地球化学]