Absolute partial cross sections for electron-impact ionization of H2, N2, and O2 from threshold to 1000 eV

Absolute partial cross sections from threshold to 1000 eV are reported for electron-impact ionization of H2, N2, and O2. Data are presented for the production of H2+ and H+ from H2; the production of N2+, N++N22+, and N2+ from N2; and the production of O2+, O++O22+, and O2+ from O2. The product ions are mass analyzed with a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output provides clear evidence that all energetic fragment ions are collected. The overall uncertainty in the absolute cross-section values for singly charged parent ions is ±3.5% and is marginally higher for fragment ions. Previous cross-section measurements are compared to the present results. copyright 1996 The American Physical Society