OBJECTIVES. KEPLER HAS REVEALED FREQUENT SUPERFLARES ON SOLAR-TYPE STARS PROVIDING A MECHANISM BY WHICH HOST STARS MAY HAVE PROFOUND EFFECTS ON THE PHYSICAL AND CHEMICAL EVOLUTION OF EXOPLANETARY ATMOSPHERES. WHAT EFFECT DO EXTREME ENERGY FLUXES FROM ERUPTIVE EVENTS DURING EARLY STELLAR EVOLUTION TOGETHER WITH UV LIGHT HAVE ON PREBIOTIC CHEMISTRY IN PARTICULAR ON THE PRODUCTION OF SMALL MOLECULE PRECURSORS CURRENTLY THOUGHT NECESSARY FOR NUCLEOSIDE SYNTHESIS AND BY CONSEQUENCE THE ORIGIN OF LIFE ON PRIMITIVE PLANETS? THIS MAY BE IMPORTANT IN TERRESTRIAL PLANETARY ATMOSPHERES WHERE SPECIES SUCH AS MOLECULAR NITROGEN AND CARBON DIOXIDE WOULD REQUIRE HIGH ENERGY IRRADIATION IN ORDER FOR THEM TO BE RECOMBINED INTO REACTIVE SPECIES SUCH AS HCN AND NOX THE FORMER OF WHICH IS CONSIDERED CRUCIAL FOR NUCLEOSIDE FORMATION AN OUTSTANDING CHALLENGE IN THE FIELD. OUR PROPOSAL AIMS TO ADDRESS THESE MAJOR QUESTIONS BY PERFORMING COMPUTATIONAL AND EXPERIMENTAL STUDIES ON THE EFFECTS OF IONIZING RADIATION INITIATED BY ENERGETIC ERUPTIVE EVENTS INCLUDING SUPERFLARES FROM YOUNG STARS AND ASSOCIATED PARTICLE EVENTS ON THE PREBIOTIC CHEMISTRY OF THE EARLY EARTH AND ITS TWINS. FIRST WE WILL CALIBRATE ATMOSPHERIC PHOTO-COLISSIONAL CHEMICAL MODELS USING EXPERIMENTAL CHARACTERIZATION OF GAS AND AQUEOUS PHASE CHEMISTRY. SECOND WE WILL CHARACTERIZE THE PROCESSES OF NITROGEN FIXATION AND THE CHAIN OF REACTIONS PRODUCING NOX N2O HCN AND OTHER N-CONTAINING SPECIES IN A GAS- AND LATER LIQUID-PHASE THAT MAY EVENTUALLY FORM ORGANIC MOLECULES OF VARYING DEGREES OF COMPLEXITY ESPECIALLY THOSE RELEVANT IN THE PREBIOTIC SYNTHESIS OF NUCLEOSIDES NOTABLY RNA. METHODOLOGY. WE WILL EMPLOY OUR 1D PHOTO-COLLISIONAL ATMOSPHERIC CHEMISTRY MODEL TO COMPUTE THE CHEMICAL FORMATION RATES OF COMPLEX ORGANIC MOLECULES INCLUDING O- AND N-CONTAINING HYDROCARBONS IN THE GAS PHASE. THESE SIMULATIONS WILL ALLOW TO US INVESTIGATE THE VIABLE PHOTOCHEMICAL MECHANISMS FOR NITROGEN AND OXYGEN FIXATION INTO COMPLEX ORGANIC MOLECULES IN THE ATMOSPHERES OF EARLY EARTH AND MARS. THESE SIMULATIONS WILL PROVIDE GUIDANCE IN EXPERIMENTS THAT EXPLORE THE STEADY-STATE GAS COMPOSITION OF N2/CO2/H2O GAS MIXTURES ALONE AND IN COMBINATION WITH MINOR AMOUNTS OF CO OR CH4 EXPOSED TO A VARIETY OF ENERGY SOURCES INCLUDING PARTICLES ELECTRIC DISCHARGES AND UV LIGHT AS WELL AS THE NATURE OF THE WATER SOLUBLE SPECIES WHEN GENERATED IN THE PRESENCE OF AN AQUEOUS PHASE HELD AT VARIOUS PH VALUES THAT SIMULATE PRIMITIVE PLANETARY STANDING WATER BODIES. EXPERIMENTAL STUDIES WILL BE CONDUCTED BY FLOWING 0.1 TO 1 ATM TOTAL PRESSURE GAS MIXTURES CONTAINING VARIOUS PARTIAL PRESSURES OF CO2 AND N2 TOGETHER WITH ADMIXTURES OF LESSER AMOUNTS OF H2O CO H2 OR CH4. THESE WILL BE IRRADIATED BY A PROTON GUN UV LAMP AND ELECTRIC DISCHARGE. STEADY-STATE GAS COMPOSTIONS WILL BE MEASURED DOWNSTREAM FROM THE REACTION CHAMBER USING A RESIDUAL GAS ANALYZER. SOLUBLE SPECIES WILL BE MEASURED USING ION CHROMATOGRAPHY DIRECT INFUSION TIME-OF-FLIGHT MASS SPECTROMETRY SPECTROSCOPICALLY USING NMR AND CHEMICALLY WITH VARIOUS ASSAYS. RELEVANCE TO EXOBIOLOGY PROGRAM. THE PROPOSED STUDIES WILL PROVIDE SIGNIFICANT IMPLICATIONS FOR THE CONDITIONS SETTING STAGE FOR THE ORIGIN OF LIFE ON EARTH THE RESOLUTION OF THE FYS ON THE EARLY EARTH/MARS AND HABITABILITY CONDITIONS ON TERRESTRIAL PLANETS AROUND YOUNG STARS. AS A SOURCE OF PREBIOTIC NITROGEN THIS WORK IS RELEVANT TO THE RESEARCH AREA OF PREBIOTIC EVOLUTION . ABIOTIC NITROGEN FIXATION IS ONE OF THE PLANETARY AND MOLECULAR PROCESSES THAT SET THE PHYSICAL AND CHEMICAL CONDITIONS WITHIN WHICH LIVING SYSTEMS MAY HAVE ARISEN BY HELPING TO UNDERSTAND HOW PLANETARY NITROGEN BECAME AVAILABLE FOR USE IN THE ORIGIN AND EARLY EVOLUTION OF LIFE. OUR UNDERSTANDING OF THE GLOBAL SCALE OF NITROGEN FIXATION WILL HELP MODEL EARLY ENVIRONMENTS ON THE EARTH IN WHICH ORGANIC CHEMICAL SYNTHESIS COULD OCCUR AND MAY SHED LIGHT ON THE PREBIOTIC SYNTHESIS OF NUCLEOSIDES LIKE RNA.