INTRODUCTION: SELF-SHIELDING OF CO IS PRESENTLY THE PREFERRED MECHANISM FOR EXPLAINING THE 60 PERMIL ENRICHMENT IN 17O AND 18O MEASURED IN TERRESTRIAL PLANETS AND METEORITES RELATIVE TO THE SOLAR PHOTOSPHERE. PREVIOUS SELF-SHIELDING MODELS HAVE USED A WAVELENGTH-INDEPENDENT APPROXIMATION KNOWN AS SHIELDING FUNCTIONS TO COMPUTE O ISOTOPE FRACTIONATION IN THE NEBULA. THROUGH PREVIOUS NASA GRANTS WE HAVE COMPILED A SET OF VERY HIGH QUALITY FUV CROSS SECTIONS FOR CO ISOTOPOLOGUES. WITH THESE DATA WE CAN QUANTITATIVELY EVALUATE CO SELF-SHIELDING FOR A RANGE OF NEBULAR LOCATIONS AND FOR ANY STELLAR FUV SPECTRUM. TO DO THIS WE MUST FIRST COMPLETE THE REDUCTION OF OUR ISOTOPIC CO CROSS SECTION DATA. WE ALSO NEED QUANTUM YIELD MEASUREMENTS FOR THE VERY IMPORTANT CO E(0) BAND. AS A PARALLEL EFFORT AND WITH COLLABORATORS WE WILL DEVELOP A COUPLED-CHANNEL (CSE) MODEL FOR CO ISOTOPOLOGUE CROSS SECTIONS INFORMED BY OUR DATA THAT WILL ALLOW US TO MODEL CO ISOTOPOLOGUE ABSORPTION SPECTRA AT THE FULL RANGE OF TEMPERATURES NEEDED FOR SOLAR NEBULA MODELING. WITH OUR CO ISOTOPIC CROSS SECTIONS WE WILL EVALUATE O AND C ISOTOPE EFFECTS DUE TO SELF-SHIELDING. A CSE MODEL ALREADY EXISTS FOR N2 AND WILL BE USED TO MODEL N2 SELF-SHIELDING TO PREDICT D15 FOR HCN AND NH3 PRODUCED PHOTOCHEMICALLY IN THE NEBULA. OUR NEBULA MODELS WILL BE RUN WITH SEVERAL FORMS OF TURBULENT TRANSPORT TO REFLECT THE RECENT WORK ARGUING THAT THE MAGNETOROTATIONAL INSTABILITY MAY BE LESS IMPORTANT THAN PREVIOUSLY BELIEVED DUE TO DISSIPATIVE EFFECTS. FINALLY WE WILL MAKE A PRELIMINARY ASSESSMENT OF THE TRANSFER OF O ISOTOPE SIGNATURES IN WATER TO NEBULAR SILICATES. PROPOSED RESEARCH: 1. O ISOTOPES. THIS TASK IS COMPOSED OF SEVERAL SUBTASKS. I) COMPLETE ANALYSIS OF OUR ISOTOPIC CO CROSS SECTION DATA. THIS IS IN COLLABORATION WITH OUR COLLEAGUES IN THE US AND FRANCE. II) MEASURE ISOTOPE-DEPENDENT QUANTUM YIELDS FOR THE E(0) BAND OF CO. THIS IS THE STRONGEST DISSOCIATING CO BAND AND THE PRESENT UNCERTAINTY IN QUANTUM YIELDS IS INTRODUCING LARGE UNCERTAINTIES INTO NEBULAR MODEL RESULTS. III) MEASURE THE ABSORPTION SPECTRUM OF 12C16O AT 1000 K. IV) DEVELOP A CSE MODEL FOR CO CROSS SECTIONS FROM 90 TO 110 NM. THIS WILL PERFORMED IN COLLABORATION WITH EUROPEAN COLLABORATORS. V) RUN SOLAR NEBULA MODEL WITH FULL O ISOTOPE CO CROSS SECTIONS. 2. C ISOTOPES. ADD C ISOTOPES TO SOLAR NEBULA MODEL. RUN USING FULL CO CROSS SECTIONS. 3. N ISOTOPES. EVALUATION OF 15N ENRICHMENT DUE TO N2 SELF-SHIELDING IN THE SOLAR NEBULA. THE D15N ENRICHMENT OF THE TERRESTRIAL PLANETS AND METEORITES INCLUDING HOT SPOTS IS WELL KNOWN. WE WILL MODEL THESE EFFECTS DUE TO N2 SELF-SHIELDING USING HIGHLY PRECISE N2 CROSS SECTIONS. 4. NEBULAR SILICATES. EVALUATE O ISOTOPE EXCHANGE OF NEBULAR WATER WITH SILICATES AND CAIS. TO EXPLAIN THE INNER SOLAR SYSTEM VIA SELFSHIELDING NEBULAR SILICATES HAD TO EXCHANGE O WITH H2O. WE HAVE PREVIOUSLY ARGUED THAT SUCH EXCHANGE IS SLOW FOR CAIS. HERE WE WILL EVALUATE EXCHANGE QUANTITATIVELY FOR CHONDRULES AND CAIS.