EOIM-III MASS-SPECTROMETRY AND POLYMER CHEMISTRY - STS-46, JULY-AUGUST 1992

The Evaluation of Oxygen Interactions with Materials III space-flight experiment was developed to obtain benchmark atomic-oxygen reactivity data and wits conducted during Space Transportation System Mission 46. We present an overview of the flight experiment and the results of th e Lyndon B. Johnson Space Center polymer chemistry and mass-spectromet er-carousel experiments. Mass-spectrometric measurements of gaseous pr oducts formed by O-atom reaction with C-13-labeled Kaptan(TM) revealed CO, CO2, H2O, NO, and NO2. By operating the mass spectrometer to dete ct naturally occurring ionospheric species, we characterized the ambie nt ionosphere at various times during the flight experiment and detect ed the gaseous reaction products formed when ambient ions interacted w ith the C-13 Kapton carousel sector, Direct comparison of the results of on-orbit O-atom exposures with those conducted in ground-based labo ratory systems, which provide known O-atom fluences and translational energies, demonstrated the strong translational-energy dependence of O -atom reactions with a variety of polymers. A line-of-centers reactive scattering model was shown to provide a reasonably accurate descripti on of the translational-energy dependence of polymer reactions with O atoms at high atom kinetic energies, and a Beckede-Ceyer model provide d an accurate description of O-atom reactivity over a three-order-of-m agnitude range in translational energy and a four-order-of-magnitude r ange in reaction efficiency. Postflight studies of the polymer samples by x-ray photoelectron spectroscopy and infrared spectroscopy demonst rate that O-atom attack is confined to the near-surface region of the sample, that is, within 50 to 100 Angstrom of the surface.