Reactive and Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

Abstract

We have investigated the scattering and reactive dynamics of a carbon fiber network at high surface temperatures. The experiments were performed with ground state atomic oxygen (O) and molecular oxygen (O2) with surface temperatures ranging from 1023 K to 1823 K. A molecular beam containing neutral O and O2 with a mole ratio of 0.92:0.08 and nominal velocity of 8 km/s was directed at the surface and the translational energy distributions of the scattered products were collected at various scattering angles and surface temperatures with the use of rotatable mass spectrometer detector. The signals from oxygen atoms exhibited impulsive scattering and thermal desorption with the thermal desorption signals increasing with surface temperature while the impulsive scattering component remained relatively constant. The O2 signals contained impulsive scattering and thermal desorption channels which were invariant to surface temperature. The dominant reactive product was CO, and CO2 was a minor product of reaction. The impulsive scattering signals were absent in CO and CO2 and both these products contained strong thermal desorption signals. The flux of CO increased with temperature but exhibited non-Arrhenius behavior where it reached a plateau at the highest temperature. Thermal CO products were observed to exit the sample promptly or after relatively long residence times and two populations of CO with long residence times were distinguished. Signatures of thermal processes occurring over long residence times were also observed for O. Hysteresis was observed in the thermal flux of O and CO with opposing trends for the two species. This work follows a similar study in our laboratory where the material in focus was vitreous carbon and the similarities and differences between the reactive dynamics of the two carbon surfaces are explored in this article.