DISSOCIATIVE ELECTRON-ATTACHMENT TO CO2

The 4.4 eV dissociative electron attachment peak in CO;? was reinvesti gated paying particular attention to (i) its structure associated with vibrational excitation and to (ii) the temperature dependence of the onset. For this purpose we have used two specially designed crossed be ams machines, one having a trochoidal electron analyzer (TEM) and one with a hemispherical electron analyzer (HEM) for the production of the highly monochromatized electron beams (with FWHM's down to 5 and 50 m eV, respectively). The present results confirm the earlier findings in (i) interpreting the dominant structures of the 4.4 eV peak as being due to vibrationally excited states of CO in the reaction CO2 + e --> O- + CO and (ii) assigning the much weaker and narrower structures to the intermediate CO,. In the temperature range between 300 and 245 K a lmost no temperature dependence of the onset can be seen in the presen t study. In comparison to NO and CO where the onset is vertical the CO 2 threshold behavior is less steep indicating that in the CO2 case a d ifferent type of transition must be responsible for the onset of the O - production. Besides DA to CO2 we have for comparison and calibration purposes investigated also DA to CO and NO.