We have undertaken a series of experiments to learn the mechanisms of carbon oxidation over a wide range of temperatures that extend to the conditions encountered during atmospheric re-entry, with a particular interest in understanding how these mechanisms change with temperature. We report here the hyperthermal scattering dynamics of ground-state atomic oxygen, O( 3 P), and molecular oxygen, O 2 ( 3 Σ g − ), on vitreous carbon surfaces at temperatures from 600 to 2100 K. A molecular beam containing neutral O and O 2 in a mole ratio of 0.93:0.07 was prepared with a nominal velocity of 7760 m s −1 , corresponding to a translational energy of 481 kJ mol −1 for atomic oxygen. This beam was directed at a vitreous carbon surface, and angular and translational energy distributions were obtained for inelastically and reactively scattered products with the use of a rotatable mass spectrometer detector. Unreacted oxygen atoms exited the surface through both impulsive scattering and thermal desorption. The preferred scattering process changed from impulsive scattering to thermal desorption as the surface temperature increased. O 2 scattered mainly impulsively from the surface, and its scattering dynamics were essentially unaffected by surface temperature. The predominant reactive product was carbon monoxide (CO). Carbon dioxide (CO 2 ) was also formed at lower surface temperatures. The flux of the CO product rose with temperature to a maximum at approximately 1500−1900 K, depending on heating rate, and then decreased with increasing surface temperature. The CO 2 flux dropped dramatically with increasing surface temperature and was below detectable limits above 1100 K. A minor reactive pathway was identified that produced O 2 , presumably through a direct Eley−Rideal reaction of an incident oxygen atom with an O atom residing on the surface. Decreased oxygen surface coverage at higher temperatures was found to limit the reactivity of the surface by inhibiting the production of CO and CO 2 at very high surface temperatures. The observed inelastic and reactive scattering behavior reveals a complex interplay between reactivity and surface temperature.

Background  People with severe intellectual disability are considered vulnerable to exploitation in research. Discovery of exploitative practices in recent history has motivated the development of guidelines for informed consent and proxy decision‐making procedures when involving these individuals in research. Methods  Issues for determining capability to provide informed consent and the proxy decision process are reviewed according to the literature, current ethics guidelines and recent legislature in Victoria, Australia. Results  The complex process of involving in research people with severe intellectual disability who are particularly vulnerable by virtue of their institutionalized residential status is discussed within the context of a recent project into examining potential nutritional determinants of Pica behaviour (i.e. the eating of inedible items). Conclusions  This example serves to highlight the role of legislation, various government bodies and researchers in balancing principles of protection of vulnerable groups and rights to self‐determination.

Interactions of ground-state atomic and molecular oxygen, O( 3 P) and O 2 ( 3 Σ g −), with a highly oriented pyrolytic graphite surface were investigated for a broad range of surface temperatures from 1100 K to approximately 2300 K. A molecular beam composed of 89% O atoms and 11% O 2 , with average translational energies of 472.1 and 944.4 kJ mol −1 , respectively, was directed at the surface with an incidence angle, θ i , of 45°. Angle-and velocity-resolved distributions were collected for nonreactively and reactively scattered products with the use of a rotatable mass spectrometer detector. Four scattered products were observed: O, O 2 , CO, and CO 2 . O atoms that exited the surface without reacting exhibited both impulsive scattering (IS) and thermal desorption (TD) components. The primary reaction product observed was carbon monoxide (CO). Carbon dioxide (CO 2 ) was measured only with surface temperatures below 1400 K, and O 2 was attributed to IS of O 2 that was present in the incident beam. Although there is evidence for either Eley−Rideal or hot atom reactions, CO and CO 2 were primarily formed by Langmuir−Hinshelwood (LH) reactions. However, the flux angular distributions of the LH products were significantly narrower than a cosine distribution, and the final energies were much higher than those predicted by the Maxwell−Boltzmann distribution characterized by the surface temperature. These observations indicate that CO and CO 2 that were produced by LH reactions desorb from the surface over a barrier. The desorption barrier of CO was determined by using the principle of detailed balance (where the desorption and adsorption barriers are equal) and was found to increase from 121 ± 5 kJ mol −1 at 1100 K to 155 ± 7 kJ mol −1 at 1300 K. As the surface temperature increased, the fluxes of CO and CO 2 produced by LH mechanisms decreased. Simultaneously, the flux of O atoms that scattered via the TD channel increased, which reduced the surface oxygen coverage at higher temperatures. The combination of reduced O-atom surface coverage and increased desorption barriers for CO suppresses the reactivity of the surface at high temperatures.

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We have conducted investigations of the energy transfer dynamics of atomic oxygen and argon scattering from hydrocarbon and fluorocarbon surfaces. In light of these results, we appraise the applicability and value of a kinematic scattering model, which views a gas-surface interaction as a gas-phase-like collision between an incident atom or molecule and a localized region of the surface with an effective mass. We have applied this model to interpret the effective surface mass and energy transfer when atoms strike two different surfaces under identical bombardment conditions. To this end, we have collected new data, and we have re-examined existing data sets from both molecular-beam experiments and molecular dynamics simulations. We seek to identify trends that could lead to a robust general understanding of energy transfer processes induced by collisions of gas-phase species with liquid and semi-solid surfaces.