Absolute total and partial electron impact ionization cross sections of hexamethyldisiloxane

R. Basner, R. Foest, M. Schmidt, K. Becker, H. Deutsch

Research output: Contribution to journalArticlepeer-review


We studied the electron impact ionization of hexamethyldisiloxane (HMDSO), Si2O(CH3)6, which is widely used in plasma-enhanced polymerization applications. Appearance energies and absolute partial cross sections for the formation of fragment ions with relative intensities > 1% of the most abundant ion, the Si2O(CH3)+5 fragment ion, were measured in a high resolution double focusing sector field mass spectrometer with a modified ion extraction stage for electron energies from threshold to 100 eV. Dissociative ionization was found to be the dominant process. The main ionization channel removes a complete methyl group to produce the fragment ion Si2O(CH3)+5 with a cross section of 1.7 × 10-15 cm2 at 70 eV. The stoichiometric and isotope composition of the various fragment ions was determined by using the high resolution (m/Δm = 40,000) of the mass spectrometer used in these studies. The methyl ion is formed with considerable excess kinetic energy, whereas all other fragment ions are formed with essentially no excess energy. The experimental total single ionization cross section of HMDSO (2.2 × 10-15 cm2 at 70 eV impact energy) is in good agreement with the result of a semiempirical calculation (2.1 × 10-15 cm2 at the same energy).

Original languageEnglish (US)
Pages (from-to)245-252
Number of pages8
JournalInternational Journal of Mass Spectrometry
Issue number3
StatePublished - Jul 1998


  • Cross sections
  • Electron impact ionization
  • Hexamethyldisiloxane
  • Plasma polymerization

ASJC Scopus subject areas

  • Instrumentation
  • Condensed Matter Physics
  • Spectroscopy
  • Physical and Theoretical Chemistry


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