Types of Stable Isotope Fractionation: Kinetic vs. Equilibrium Fractionation скачать в хорошем качестве

Types of Stable Isotope Fractionation: Kinetic vs. Equilibrium Fractionation

Equilibrium fractionation occurs when isotopes of an element are distributed between two or more substances in a reversible reaction, reaching a state of dynamic balance. At equilibrium, the isotopes are partitioned based on differences in their chemical bond strengths, often resulting in the heavier isotope being preferentially concentrated in the substance with the stronger bonds. This type of fractionation is temperature-dependent, with greater fractionation observed at lower temperatures. Example: The distribution of oxygen isotopes between water and carbonate minerals, where heavier oxygen-18 isotopes tend to be more concentrated in the minerals compared to water. Kinetic fractionation happens during irreversible processes where the reaction rates differ for isotopes due to their mass differences. Lighter isotopes typically react or diffuse more quickly than heavier ones, leading to their preferential incorporation into reaction products or escaping substances. This type of fractionation is not dependent on equilibrium conditions but rather on the speed and direction of the reaction or physical process. Example: The evaporation of water, where lighter hydrogen and oxygen isotopes (e.g., hydrogen-1 and oxygen-16) evaporate more readily than their heavier counterparts (e.g., deuterium and oxygen-18), resulting in vapor that is enriched in lighter isotopes. References Hoefs, J. (2009). Stable Isotope Geochemistry (6th ed.). Springer. This book provides a detailed explanation of both equilibrium and kinetic isotope fractionation. Sharp, Z. (2007). Principles of Stable Isotope Geochemistry. Pearson Prentice Hall. This textbook offers a comprehensive overview of the principles behind isotope fractionation, including examples and applications. Criss, R. E. (1999). Principles of Stable Isotope Distribution. Oxford University Press. This reference discusses the underlying mechanisms and applications of different types of isotope fractionation in geochemical processes.