- Reactions of Ar+, Ne+, and He+ with SiF4 from thermal energy to 50 eV c.m.
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Guided ion-beam techniques are used to measure the cross sections for reaction of SiF4 with Ar+, Ne+, and He+ from thermal to 50 eV.Charge transfer followed by loss of F atoms are the sole processes observed.All SiFx+
- Weber, M. E.,Armentrout, P. B.
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- Electron impact ionization cross sections of SiF2
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Absolute cross sections are measured for electron impact ionization and dissociative ionization of SiF2 from threshold to 200 eV.A fast (3 keV) neutral beam of SiFz is formed by charge transfer neutralization of SiF2+ with Xe; it is primarily in the ground electronic state with about 10percent in the metastable first excited electronic state (3B1).The absolute cross section for ionization of the ground state by 70 eV electrons to the parent SiF2+ is 1.38 +/- 0.18 Angstroem2.Formation of SiF+ is the major process with a cross section at 70 eV of 2.32 +/- 0.30 Angstroem2.The cross section at 70 eV for formation of the Si fragment ion is 0.48 +/- 0.08 Angstroem2.Ion pair production contributes a significant fraction of the positively charged fragment ions.
- Shul, Randy J.,Hayes, Todd R.,Wetzel, Robert C.,Baiocchi, Frank A.,Freund, Robert S.
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- Energetics and dynamics in the reaction of Si+ with SiF4. Thermochemistry of SiFx and SiF+x (x=1, 2, 3)
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The title reaction is studied using guided ion beam mass spectrometry.Absolute reaction cross sections are measured as a function of kinetic energy from thermal to 40 eV, and three endothermic product channels are observed.The dominant SiF+ + SiF3 channel is only slightly endothermic, while the SiF3+ + SiF and SiF2+ + SiF2+ channels have much higher thresholds.The SiF3+ cross section magnitude is about half that of SiF+, while the SiF2+ cross section is an order of magnitude smaller than that of SiF+.A second feature which appears in the SiF2+ cross section is due to dissociation of SiF3+ .There is evidence that SiF+ and SiF3+ are produced via a direct mechanism.Competition between these two channels is interpreted in terms of molecular orbital correlations and qualitative potential energy surfaces.One surface is found to correlate only with the SiF3+ + SiF channel, while another correlates diabatically with this channel and adiabatically with the SiF+ + SiF3 channel.Competition on this latter surface has an energy dependence which is consistent with the Landau-Zener model.Reaction thresholds are analyzed to yield 298 K heats of formation for SiFx and SiFx+ species.From an evaluation of these and literature values, we recommend the following values:.
- Weber, M. E.,Armentrout, P. B.
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p. 6898 - 6910
(2007/10/02)
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- Electron-impact ionization cross sections of the SiF3 free radical
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Absolute cross sections for electron-impact ionization of the SiF3 free radical from threshold to 200 eV are presented for formation of the parent SiF3 ion and the fragment SiF2 , SiF+, and Si+ ions.A 3 keV beam of SiF3 is prepared by near-resonant charge transfer of SiF3 with 1,3,5-trimethylbenzene.The beam contains only ground electronic state neutral radicals, but with as much as 1.5 eV of vibrational energy.The absolute cross section for formation of the parent ion at 70 eV is 0.67 +/- 0.09 Angstroem2.At 70 eV the formation of SiFi2+ is the major process, having a cross section 2.51 +/- 0.02 times larger than that of the parent ion, while the SiF+ fragment has a cross section 1.47 +/- 0.08 times larger than the parent.Threshold measurements show that ion pair dissociation processes make a significant contribution to the formation of positively charged fragment ions.
- Hayes, Todd R.,Shul, Randy J.,Baiocchi, Frank A.,Wetzel, Robert C.,Freund, Robert S.
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p. 4035 - 4041
(2007/10/02)
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