WE PROPOSE HERE TO CONTINUE MODELING THE PHOTOCHEMICAL ESCAPE FLUXES AND RATES OF THE ATOMS 16O 12C AND 14N FROM THE MARTIAN ATMOSPHERE USING AN ENHANCED VERSION OF A MONTE CARLO ESCAPE CODE THAT WE HAVE DEVELOPED WITH PREVIOUS FUNDING. WE WILL ALSO DETERMINE THE ISOTOPE EFFECTS INHERENT IN THE MECHANISMS WHICH OPERATE IN ADDITION TO ANY FRACTIONATION DUE TO DIFFERENCES IN THE ALTITUDE PROFILES OF THE ISOTOPOMERS INVOLVED IN THE NON-THERMAL ESCAPE MECHANISMS. WE WILL DO THIS BY DETERMINING THE ESCAPEPROBABILITIES FOR 18O 17O 13C AND 15N AND COMPARING THEM TO THOSE OF THE MAJOR ISOTOPES. UNDER THE CURRENT GRANT WE HAVE COMPUTED THE ESCAPE FLUX OF 16O DUE TO DISSOCIATIVE RECOMBINATION (DR) OF O2+ AND THE PROBABILITY OF ESCAPE OF 18O FOR TWO MODELS:60 DEGREE SOLAR ZENITH ANGLE LOW AND HIGH SOLAR ACTIVITY MODELS. WE HAVE FOUND (SURPRISINGLY AND IN CONTRAST TO THE CONVENTIONAL WISDOM) THAT THERE IS A LARGE FRACTIONATION FACTOR OF 0.2 TO 0.37 FROM 150 TO 300 KM INHERENT IN THE DR MECHANISM. WE HAVE ALSO SHOWN THAT THE EXOBASE APPROXIMATION FAILS TOTALLY FOR ESCAPE OF O SINCE THE FRACTION OF ESCAPING O ATOMS ARISING FROM BELOW THE EXOBASE IS GREATER THAN 0.9. WE HAVE ALSO COMPLETED THE CALCULATIONS FOR 4 OF THE 7 PHOTOCHEMICAL ESCAPE MECHANISMS FOR C. IN THE PERIOD OF THE PROPOSED INVESTIGATION WE WILL: ADD INELASTIC PROCESSES TO THE O ESCAPE CALCULATIONS AND THE ABILITY FOR THE PROJECTILE TO CHANGE IDENTITIES; DETERMINE THE 13C/12C ISOTOPE EFFECTS INHERENT IN THE MECHANISMS; WE WILL CARRY OUT CALCULATIONS FOR PHOTOCHEMICAL ESCAPE FLUXES OF 14N AND THE 15N/14N ISOTOPE FRACTIONATION FACTORS INHERENT IN THE MECHANISMS; WE WILL CARRY OUT CALCULATIONS FOR VARIOUS LATITUDES LOCAL TIMES SOLAR ZENITH ANGLES AND SEASONS; WE WILL MODEL THE ANCIENT IONOSPHERES (AT 2.5 GYR AND 3.5 GYR BEFORE PRESENT)USING NEUTRAL THERMOSPHERES FROM COLLABORATOR S. BOUGHER. THE MODEL ATMOSPHERES ARE VERTICAL SLICES OF HIS MARS THERMOSPHERIC GENERAL CIRCULATION MODEL (MTGCM). FINALLY USING ESTIMATES OF OTHER NON-THERMAL ESCAPE MECHANISMS WE WILL INTEGRATE BACKWARD IN TIME TO DETERMINE THE ISOTOPE RATIOS AT ABOUT 3.8 GYR AT THE END OF THE CATASTROPHIC PERIOD IN THE HISTORY OF MARS. THIS PROJECT SEEKSTO ANSWER "THE FUNDAMENTAL SCIENTIFIC QUESTION" OF "HOW THE CLIMATE OF MARS HAS EVOLVED OVER TIME TO REACH ITS CURRENT STATE" (MEPAG GOAL II LINE 1). IT IS MOST RELEVANT TO MEPAG GOAL II.C.1 "DETERMINE THE RATES OF ESCAPE OF KEY SPECIES FROM THE MARTIAN ATMOSPHERE AND THEIR CORRELATION WITH SEASONAL AND SOLAR VARIABILITY".