Molecular beam studies of hyperthermal atomic oxygen and argon interactions with polymer surfaces and gas-phase molecules.

摘要

O atoms and N2 molecules in the outer atmosphere of the Earth collide with spacecraft surfaces and various gases that are released from space vehicles. The high relative velocity of the collisions promotes high reaction probability and large energy transfers, leading to materials degradation and chemiluminescent reactions, which may interfere with the mission of the vehicle. The work presented in this thesis uses sophisticated molecular beam and surface science techniques to study materials degradation and individual reactive and inelastic collisions in an effort to understand the complex chemistry and physics that are characteristic of space vehicle interactions with Earth's upper atmosphere. A new space-durable polymer, polyhedral oligomeric silsesquioxane polyimide, has been identified. When exposed to atomic oxygen, this polymer forms a protective SiO2 layer on its surface. Beam-surface scattering experiments showed that collision-induced dissociation becomes an important gas-surface process when the translational energy of the incident atom or molecule is greater than 8 eV. Experiments on the dynamics of gas-phase collisions at hyperthermal collision energies found that inelastic collisions may transfer large amounts of energy into internal degrees of freedom. The scattering dynamics of the reactive 16OC product from the 16O( 3P) + C18O → 16OC + 18O reaction were quite unexpected, with 16OC predominantly forward scattered. Experiments on the reactions of O( 3P) with H2O demonstrated the occurrence of a previously unobserved reaction pathway, O(3P) + H2O → HO2 + H, with a barrier determined to be ∼2.6 eV. These studies of hyperthermal processes with molecular beam techniques have enabled us to identify a promising new material and to understand the detailed collision dynamics in model gas-surface and gas-phase systems. In each case, the experiments have revealed new chemical or energy transfer processes that were not considered earlier. These previously unknown processes reveal trends in hyperthermal collisions that will undoubtedly be critical to the planning and design of missions that put space vehicles in contact with the outer reaches of the Earth's atmosphere.