Absolute partial cross sections for electron-impact ionization of NO and NO2 from threshold to 1000 eV

Absolute partial cross sections for electron-impact ionization of nitric ox ide and nitrogen dioxide are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output d emonstrates that all product ions are collected irrespective of their initi al kinetic energy. Data are presented for the production of NO+, N+, O+, an d NO2+ ions from NO; and for the production of NO2+, NO+, N+, O+, and (N2+O2+) ions from NO2. The overall uncertainty in the absolute cross section v alues is +/- 5% for singly charged parent ions, while that for the fragment ions may be as large as +/- 20%. For NO, the previously published data are generally in reasonable agreement with those presented here, although ther e remain some significant discrepancies with even the most recent work. No previous comprehensive study of NO2 has apparently been reported but the ex perimental NO2+ cross section data that are available disagree substantiall y with the present measurements. The present total NO2 cross section is, ho wever, in excellent agreement with recent theoretical work. (C) 2000 Americ an Institute of Physics. [S0021- 9606(00)01521-X].