MEASUREMENTS

MULTIPHOTON IONIZATION (MPI) AND LASER-INDUCED FLUORESCENE (LIF) HAVE BEEN PROPOSED TO DETECT VIBRATIONALLY EXCITED STATES OF GROUND AND METASTABLE EXCITED ELECTRONIC STATES OFN2 AND O2. SUCH SPECIES AS O2(A1 ), N2(A3 ), AND N2(X,V>>0)MAY BE PRODUCED AND FURTHER EXCITED IN THE SHOCK LAYER OF SPACECRAFT UNDERGOING HIGH ALTITUDE REENTRY. THE QUENCHING OF THESE SPECIES ON SPACECRAFT SURFACES MAY RESULT IN ADDITIONAL HEAT LOAD ON THE VEHICLE. IN PHASE I RESEARCH WEWILL DEMONSTRATE THE ABILITY TO DETECT O2 (A1 ) AND N2(X,V) USING MPI AND N2(A3 ) USING LIF IN A DISCHARGE FLOW REACTOR LINED WITH VARIOUS SPACECRAFT MATERIALS. THE REACTOR WILL BE USED TO CONDUCT SCREENING TESTS TO OBTAIN 300K SURFACE DEACTIVATION COEFFICIENTS FOR THESE MOLECULES. PHASE I EFFORTS WILL ALSO FOCUS ON THE DESIGN OF A MOLECULAR BEAM/SURFACE SCATTERING EXPERIMENT TO BE CONSTRUCTED UNDER PHASE II. THIS EQUIPMENT WILL USE A DISCHARGE-EXCITED SUPERSONIC MOLECULAR BEAM OF METASTABLE MOLECULES SEEDED IN HE TO ACHIEVE TRANSLATIONAL VELOCITIES IN EXCESS OF 4000K FOR O2 OR N2. THE MPI AND LIF TECHNIQUES DEMONSTRATED IN PHASE I WILL BE USED TO DETECT MOLECULES SCATTERED OFF THE SURFACES AND THE LASER POLARIZATION DEPENDENCE OF THE LIF SIGNAL WILL BE USED TO OBTAIN ANGLE INTEGRATED EXCITATION AND QUENCHING EFFICIENCIES.