Dissociative attachment in carbon dioxide

The production of O− from CO2 by dissociative attachment has been studied with electrons having energies in the range 0–20 eV. In addition to the two already well established peaks in the 0–10 eV range, a third peak has been substantiated, at 13 eV. At room temperature the 13 eV peak cross section is approximately 6 × 10−21 cm2, rising to approximately 2 × 10−20 cm2 at 1000°K. Measured O− ion kinetic energy distributions corresponding to the three processes peaking at 4.4, 8.2, and 13.0 eV are presented and their relevance to previous work is discussed. In all three processes only the high energy tails of the ion energy distributions are found to be sensitive to electron energy, with a decreasingly small fraction of the available energy appearing as kinetic energy of separation of the fragments. In this respect the results are similar to previous measurements of O− production from N2O.