GASEOUS, LIQUID, AND SUPERCRITICAL FLUID H2O AND CO2: OXYGEN ISOTOPE FRACTIONATION BEHAVIOR

Abstract

Data from published oxygen isotope exchange experiments involving H2O and CO2 have been used to determine the reduced partition function ratios of liquid and supercritical fluid H2O and CO2. These data are compared with a recalculation of the reduced partition function ratios for the vapor phase of each species. A semi-empirical approach to the experimental data yields reduced partition function ratios, 103 ln (Q*/Q)r, of the form 0.002419x3 - 0.1254x2 + 6.237x + 12.815 H2O(1) 273=<T=<403 0.1199x3 - 2.020x2 + 16.586x - 6.482 H2O(l) 403=<T=<647 0.5578x3 - 2.812x2 + 12.830x H2O(c) 673=<T=<~ - 0.09552x2 + 9.068x 21.128 CO2(l) 223=<T=<305 where x = 106/T2, and T is in Kelvin. Supercritical fluid carbon dioxide behaves similarly to CO2 vapor, but there is a measurable difference between the partitioning behavior of supercritical fluid, liquid, and gaseous H2O which must be considered when dealing with geological fluids.