Photochemical fractionation of 16O in the space medium modeled by resonance excitation of CO by H-Lyman alpha.
Inferences about the formation of primordial matter in our solar system rest on analysis of the earliest preserved materials in meteorites, of the structure of the solar system today, and of matter in evolving stellar systems elsewhere. The isotope distribution in meteorites suggests that molecular excitation processes similar to those observed today in circumstellar regions and dark interstellar clouds were operating in the early solar nebula. Laboratory model experiments together with these observations give evidence on the thermal state of the source medium from which refractory meteoritic dust formed. They indicate that resonance excitation of the broad isotopic bands of molecules such as 12C16O, MgO, O2, AlO, and OH by strong UV line sources such as H-L alpha, Mg II, H beta, and Ca II may induce selective reactions resulting in the anomalous isotopic composition of oxygen and possibly other elements in refractory oxide condensates in meteorites.