The mass-independent fractionation of oxygen: a novel isotope effect and its possible cosmochemical implications.

Experimental evidence is presented which demonstrates a chemically produced, mass-independent isotopic fractionation of oxygen. The effect is thought to result from self-shielding by the major isotopic species (16)O(2), but other possible mechanisms such as molecular symmetry cannot be ruled out. In a three-isotope plot, the experimentally produced fractionation line is essentially equal in slope to the observed carbonaceous chondrite mixing line. The implications for the early history of the solar system are discussed.