Surface Generation of Electronically Excited States of O2

摘要

This investigation of surface-related processes consisted of two parts; laboratory studies of the production and loss of electronically excited oxygen species on metallic surfaces, and an investigation of the mechanisms that might contribute to the so-called Space Shuttle glow. In the laboratory work, production by atom recombination of the states of O2 that lie between 4 and 5 eV was studied. The efficiency of their generation was correlated with the identity of the metal, its position on the periodic chart, surface temperatures, alloy composition, and the electronic heat capacity. Spectra of the emissions originating at the surfaces were shown to be non-specific to the particular metal, implying that internal energy distributions in the emitting metastable molecules were determined by gas phase interactions. Further study of surface energy accommodation, and the possible generation of highly vibrationally excited molecules is called for. The loss of O2 on metallic surfaces was investigated, and showed both similarities and differences with the production of the higher O2 states on the same surfaces. Metals in a given group of the periodic chart tend to exhibit similar temperature effects. The Space Shuttle glow study involved development of a model for the process, which has been useful in guiding the investigations as subsequent in situ experiments have been carried out. By consideration of the present status of the observations, it has been found possible to clarify which of the current explanations of the glow-forming mechanism are viable, and which must be discarded.