LI Jing, XUE Dong-mei*, WANG Yi-dong, WANG Zhong-liang

(1. Key Laboratory of Tianjin on Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China;
2. College of Geography and Environmental Sciences, Tianjin Normal University, Tianjin 300387, China)

Abstract: The model calculation of stable isotopic fractionation is an important aspect in the study of isotopic theory. Based on previous studies, we have summarized several kinds of formulas for calculating the isotopic kinetic fractionation. They include the first order dynamic reaction equation, the Michaelis-Menten (MM) kinetic equation, and the Michaelis-Menten-Monod (MMM) kinetic equation under the steady state hypothesis, and the Michaelis-Menten-Monod (TR-MMM) kinetic equation under the transition state assumption. A relatively accurate value has been obtained by calculation using the TR-MMM kinetic equation due to the loosening of the steady state hypothesis. Temperature has a significant effect on the chemical reaction rate, and then has effect on the associated isotopic fractionation coefficients. On the basis of relationship between reaction rate and thermodynamics, an indirect relationship between the isotope fractionation coefficient and thermodynamics has been established and then the corresponding equation of isotope fractionation coefficient to temperature change has been obtained.

Keywords: isotopic kinetic fractionation; first-order kinetic equation; steady state; transition state; thermodynamics

ACTA MINERALOGICA SINICA Vol. 40, No.3, 2020, page 248-254