TY - JOUR
T1 - Absolute total and partial electron impact ionization cross sections of hexamethyldisiloxane
AU - Basner, R.
AU - Foest, R.
AU - Schmidt, M.
AU - Becker, K.
AU - Deutsch, H.
N1 - Funding Information:
One of us (K.B.) would like to acknowledge financial support for this project from the U.S. National Science Foundation (NSF) under grant PHY-9722438. The authors are grateful for the technical assistance provided by U. Haeder.
PY - 1998/7
Y1 - 1998/7
N2 - 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).
AB - 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).
KW - Cross sections
KW - Electron impact ionization
KW - Hexamethyldisiloxane
KW - Plasma polymerization
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U2 - 10.1016/S1387-3806(98)14027-7
DO - 10.1016/S1387-3806(98)14027-7
M3 - Article
AN - SCOPUS:0001096840
SN - 1387-3806
VL - 176
SP - 245
EP - 252
JO - International Journal of Mass Spectrometry
JF - International Journal of Mass Spectrometry
IS - 3
ER -