Silanes ionization energies

The ionization energies of hydrogen (15.4 eV) and argon (15.8 eV) are higher than those of silane (11.6 eV) and disilane (9.9 eV). Therefore, ion-molecule reactions of H2 or Ar+ with silane or disilane will result in electron transfer from... 

The rate coefficient for electron impact ionization depends very sensitively on the ionization energy, as is demonstrated in Fig. 8. We calculated the ratio of the rate coefficients for total ionization of silane for different electron temperatures using the total ionization cross sections of Chatham et al. (1984) and Krishnakumar and Srivastava (1995). The primary difference between the two cross-section data sets at low energies is a 0.6-eV difference in the measured ionization energy [with Chatham et al. (1984) reporting the lower value]. As expected, the... 

Another simple means of creating ions is a surface ionization source. This works effectively for species having low ionization energies, which in this work include atomic silicon and atomic transition metals. Typically, a rhenium filament resistively heated to about 2200 K is used. Silane or the vapors of a transition metal complex or salt are directed at the filament, where decomposition and ionization occur. It is generally believed that the electronic state distribution of the ions formed is in equilibrium at the filament temperature. This generally produces ground-state ions, e.g., exclusively Si+( P), with a distribution of spin-orbit levels associated with the filament temperature. 

The difference in the behavior of these four ions is easily rationalized. The ionization energies (lEs) of He and Ne fall in a region where resonant ionization preferentially removes an electron from the 3ai orbital of SiH4. Photoionization studies indicate that ionization from this orbital yields Si+ and SiH " products almost exclusively (Cooper et al., 1990). In contrast, the lEs of Kr and Xe are resonant with the lower-energy 2t2 orbital of SiH4. Photoionization from this orbital results in less dissociation, preferentially forming SiHj and SiH. Thus, the dominant products observed are consistent with the photoionization results for removal of an electron from the two distinct valence molecular orbitals of silane. 

In silane discharges, one observes the following when the discharge is off, the mass spectrometric signal at m/e = 31 amu/e (SiH ) as a function of electron energy is due to dissociative ionization of SiHa in the ionizer of the QMS, with an ionization potential of 12.2 eV [312]. The signal with the discharge on is due to ionization of the radical SiHa plus the contribution from dissociative ionization... 

The total energy, the structure, and the ionization pattern of the more stable phenyl derivative have been calculated.52,33 The controlled explosion of triazide(phenyl)silane in a flash-pyrolysis apparatus under approximately unimolecular conditions (p = 10-3 Pa, c = 10 2 3 mil/) can be carried out without danger.52,53... 

FIGURE 4. (He I) Photoelectron spectra of silanes (a) Linear parent compounds Si H2 +2 with assignments asiSi or (SiH) and low energy asiSi ionization band splitting scheme (cf. text), (b) linear or cyclic permethyl-substituted silanes, Si (CIl3)2 12 or Si (( 113)2, with indicated band analysis... 

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