金刚石压腔结合拉曼光谱技术进行氢同位素分馏的实验研究

Research on the Experiment of Hydrogen Isotope Fractionation Using Diamond Anvil Cell and Raman Spectra

应用水热金刚石压腔结合拉曼光谱技术来进行石膏和重水间稳定同位素分馏的实验研究。氢同位素D与H的质量差百分比是所有稳定同位素里最大的,由质量引起的分馏更容易发生,更容易在实验中观测;石膏是浅部地壳重要的含水矿物,它与重水之间的同位素分馏效应对矿物-水体系的同位素平衡分馏研究具有重要意义。常用分馏系数是指两矿物或两物相间的同位素比值之商αA-B=RA/RB。拉曼光谱中,物质特征峰的峰强度比值与相应的物质的量的比值呈很好的线性相关,应用石膏和重水的拉曼特征峰强度比值来表征同位素分馏系数α=I(D-O)/I(H-O)石膏/I(D-O)I(H-O)重水两物相间要达到完全的同位素交换是测定稳定同位素分馏系数的前提。此研究应用化学合成法,增加体系的压力使矿物溶解,然后在不同的温度条件下降压使矿物重新结晶。重新结晶的晶体与流体间达到了完全的同位素分馏平衡,得出不同温度下的同位素分馏系数。相对于前人的研究,此方法的原位测量不破坏样品,避免了污染;同时避免了传统的淬火过程中同位素退化交换作用,达到了完全的同位素分馏平衡。金刚石压腔结合拉曼光谱法进行稳定同位素分馏的实验研究是完全可行的。

Hydrothermal diamond-anvil cell and Raman spectroscopy were used to measure the hydrogen isotope fractionation factor between gypsum and liquid water.Hydrogen isotopes of deuterium（D） and hydrogen（H） show the largest relative mass difference in all stable isotope systems.The exchange reaction between D and H would easily take place and the extent of exchange would be larger than others under same condition.So we selected the hydrogen isotopes for the investigation.The concept of fractionation factor is the quotient of ratios of heavy and light isotopes in different minerals,and can be expressed as αA-B=RA/RB.There is a linear relationship between ratio of Raman peak intensities and ratio of corresponding amount of substances.So the fractionation factor between gypsum and heavy water can be expressed asα=I（D-O）I（H-O）gypsumI（D-O）I（H-O）heavywater The experimental study for the isotope fractionation is based on the dissolution and recrystallization of minerals in aqueous solutions.The process can reach the total isotope fractionation equilibrium and get isotope fractionation factors with different temperatures.Compared with other methods,chemical synthesis one has following advantages：（1） short time for the experiment;（2） no problem about the equilibrium for isotope exchanges.It was proved that the new method would be more convenient and reliable for obtaining the isotopic fractionation factor compared with previous ways.