Electron stimulated desorption from solid CO_2 and a hydrogen containing CO_2 matrix: A comparative study

摘要

We have studied electron stimulated desorption of positive ions from approx 15 monolayer (ML) film of pure solid CO_2 adsorbed on polycrystalline Pt surface approx 40 K using incident electrons in the energy range 1-31 eV. The positive ions O~+, C~+, CO+, CO_2~+, and O_2~+ were observed and their threshold energies are discussed. Hydrogenation of the CO_2 film was found to reduce the O_2~+ production but the threshold remained the same as for the pure CO_2 matrix. After hydrogenation of the CO_2 matrix additional ions—H~+, H_3O~+, HCO~+, and H_2CO~+—are observed. The formation of formaldehyde cations (with a threshold energy of 17 +- 1.5 eV) in the hydrogenated CO_2 matrix has been observed for the first time and is a product of electron stimulated ion-molecule reactions, possibly via a process analogue to the so-called photosynthesis. These results could be relevant to a better understanding of the atmosphere of Mars.