ROOM-TEMPERATURE OXYGEN-ISOTOPE EXCHANGE BETWEEN LIQUID CO2 AND H2O

The equilibrium oxygen isotope fractionation factor for liquid carbon dioxide and water at 25.3-degrees-C is 41.94 +/- 0.27 parts per thousa nd as determined by direct exchange. Oxygen isotope exchange between t he two phases is initially very rapid with over 50% of the exchange oc curring in the first half hour. Complete exchange is only achieved aft er approximately 3 days. Both the speed of reaction between liquid car bon dioxide and water and the magnitude of the fractionation at room t emperature have important implications for oxygen isotope exchange exp eriments involving carbon dioxide where trace quantities of water may be present. Reaction between the carbon dioxide and water will enrich the carbon dioxide in O-18, modifying its initial composition in a pre dictable way.