GASEOUS, LIQUID, AND SUPERCRITICAL-FLUID H2O AND CO2 - OXYGEN-ISOTOPEFRACTIONATION BEHAVIOR

Data from published oxygen isotope exchange experiments involving H2O and CO2 have been used to determine the reduced partition function rat ios of liquid and supercritical fluid H2O and CO2. These data are comp ared with a recalculation of the reduced partition function ratios for the vapor phase of each species. A semi-empirical approach to the exp erimental data yields reduced partition function ratios, 10(3) ln (Q/ Q)(r), of the form 0.002419x(3) - 0.1254x(2) + 6.237x + 12.815 H2O(1) 273 less than or equal to T less than or equal to 403 0.1199x(3) - 2.0 20x(2) + 16.586x - 6,482 H2O(1) 403 less than or equal to T less than or equal to 647 0.5578x(3) - 2.812x(2) + 12.830x H2O(c) 673 less than or equal to T less than or equal to infinity - 0.09552x(2) + 9.068x 21 .128 CO2(1) 223 less than or equal to T less than or equal to 305 wher e x = 10(6)/T-2, and T is in Kelvin. Supercritical fluid carbon dioxid e 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 flu ids. Copyright (C) 1997 Elsevier Science Ltd.