Absolute partial cross sections for electron-impact ionization of CH₄ from threshold to 1000 eV

H. C. Straub, D. Lin, B. G. Lindsay, K. A. Smith, and R. F. Stebbings

J. Chem. Phys. 106, 4430-4435 (1997)

Absolute partial cross sections for the production of CH₄⁺, CH₃⁺, CH₂⁺, CH⁺, C⁺, H₂⁺, and H⁺ from electron-impact ionization of CH₄ 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 demonstrates that all product ions are completely collected. The overall uncertainty in the absolute cross section values is ±3.5% for singly charged parent ions and is slightly greater for fragment ions. Although previous measurements are generally found to agree well with the present results for CH₄⁺ and CH₃⁺, almost all previous work for the remaining fragment ions lies lower than the present results and in the case of H⁺ is lower by approximately a factor of 4.