Negative Ion Formation in NO2 by Electron Attachment

Negative ion formation in NO2 by electron attachment is studied at low pressures as a function of electron energy in a mass spectrometer. The principle ion formed is found to be O− which onsets at 1.35±0.05 ev and whose apparent maximum occurs at 1.90 ev. Comparison of the peak shape with the electron energy distribution indicates the maximum cross section occurs within 0.1 ev of threshold. The NO2− ion whose maximum cross section is only about one-hundredth that for O− appears to have the same energy dependence. Crude estimates of the cross section for attachment yield order of magnitude values of 10−18 cm2 for O− and 10−20 cm2 for NO2−.