In order to understand the degradation pathways suffered by protective coatings and polymeric satellite materials in the low-earth orbit (LEO) space environment, reactions of hyperthermal oxygen ions with self-assembled monolayers (SAMs) and silicon oxide thin films are studied under ultra-high vacuum (UHV) conditions.   The scattered ionic products are collected with energy-, angle- and mass-resolved detection when 5-40 eV O+ ions impact an alkanethiolate SAM. X-ray photoelectron spectroscopy (XPS) is used to measure the resulting erosion yield and degree of oxidation in the hydrocarbon layer. To learn about the site-specificity to hydrogen abstraction in this system, SAM layers are grown for which the hydrogen atoms located on the C-12, C-11, or C-10 positions of 1-dodcanethiol are substituted with deuterium atoms. By comparing the yields of OH to OD emerging from these three isotopomers, it is found that hyperthermal O+ ions initially abstract only H(D)-atoms bound to the top two carbon atoms within the SAM layer. In addition, scanning tunneling microscopy (STM) images of the irradiated SAM layer reveal that 5-eV O+ ions attack the film predominantly near domain boundaries. In contrast, large defect-free surface domains show considerable stability against 5-eV O+ bombardment.   The reaction dynamics of hyperthermal O2+ with a SiOx/Si(001) thin film is also studied. Isotopic labeling helps to identify the mechanisms leading to the anionic reaction channels. O– signals are composed of dissociative scattering and sputtering products, whereas O2– signals arise from nonreactive scattering, recoil abstraction and symmetric substitution channels. The complex dynamics associated with ion-beam oxidation of Si(001) by 5-120 eV O+ and O2+ are discussed. The cross section for oxygen incorporation is found to depend strongly on the conditions under which the underlying oxide layer was grown; the kinetic energy of the incorporating ion; and whether the incident ion is atomic or molecular oxygen.