F. W. Lampe

Ion–molecule reactions in SiH4–D2 mixtures

The ion–molecule reactions characteristic of SiH4–D2 mixtures have been elucidated and the reaction cross sections measured as a function of relative kinetic energy. D2+ reacts with SiH4 to yield SiH3+, SiH2+, SiH+, and Si+ by exothermic processes that proceed with a total cross section near the Langevin orbiting value. D3+ reacts with SiH4 to form only SiH3+ with a cross section also near the Langevin value. The absence of SiH2D+ suggests direct H− transfer from SiH4 rather than the intermediate formation of SiH4D+. All reactions of Si‐containing ions in their ground states with D2 are endothermic. Energy thresholds for the deuterium atom pickup reactions of Si+ and SiH2+ yield thermochemical results in satisfactory agreement with values obtained by other methods. SiH3+ reacts with D2 to form SiH2D+ solely, a result indicating that only HD is eliminated from an SiH3D2+ intermediate and showing the nonequivalence of D and H in the silanium ion.

The 147‐nm photolysis of hexafluoroacetone

The photochemical decomposition of (CF3)2CO by light of 147‐nm wavelength has been studied by monitoring mass spectrometrically the formation of C2F6. Addition of NO results in the formation of CF3NO and (CF3)2NOCF3 with complete suppression of C2F6, showing that formation of CF3 radicals is the only significant primary dissociation. The quantum yield of (CF3)2CO increases from a low‐pressure limit of 0.45 to 1.55 at about 10 torr and appears to have a high‐pressure limit of 2. This rather unusual pressure dependence is opposite to that generally observed in photochemical reactions and in particular to that found in the (CF3)2CO photolysis with light of wavelength greater than 260 nm. A mechanism involving activation of a second molecule of (CF3)2CO by energy transfer in a collision with a photoexcited molecule is proposed to explain the experimental results.

The reactions of Si+ ions with CH3SiH3, CH3SiD3, C2H6, and CH3CHD2

The reactions of Si{sup +} with CH{sub 3}SiH{sub 3}, CH{sub 3}SiD{sub 3}, C{sub 2}H{sub 6}, and CH{sub 3}CHD{sub 2} have been studied in a tandem mass spectrometric apparatus over the kinetic energy range of 1--10 eV laboratory-frame-of reference (LAB). In all systems, the major process is the formation of SiCH{sup +}{sub 3}, as well as SiCH{sub 2}D{sup +} and SiCHD{sup +}{sub 2} in the case of the reaction with CH{sub 3}CHD{sub 2}. It is shown that in the reaction of Si{sup +} with CH{sub 3}SiH{sub 3} and CH{sub 3}SiD{sub 3}, the process is best described as a Walden inversion, while in the reaction with C{sub 2}H{sub 6} and CH{sub 3}CHD{sub 2}, the process appears to approximate the spectator stripping model or modified spectator stripping (polarization-reflection model). In the reaction with CH{sub 3}CHD{sub 2}, the slight preference of Si{sup +} to strip the CH{sub 3} radical rather than the CHD{sub 2} radical is shown to be in accord with a cross-sectional energy dependence of approximately {ital E}{sup {minus}1}.The reactions of Si+ with CH3SiH3, CH3SiD3, C2H6, and CH3CHD2 have been studied in a tandem mass spectrometric apparatus over the kinetic energy range of 1–10 eV laboratory‐frame‐of reference (LAB). In all systems, the major process is the formation of SiCH+3, as well as SiCH2D+ and SiCHD+2 in the case of the reaction with CH3CHD2. It is shown that in the reaction of Si+ with CH3SiH3 and CH3SiD3, the process is best described as a Walden inversion, while in the reaction with C2H6 and CH3CHD2, the process appears to approximate the spectator stripping model or modified spectator stripping (polarization‐reflection model). In the reaction with CH3CHD2, the slight preference of Si+ to strip the CH3 radical rather than the CHD2 radical is shown to be in accord with a cross‐sectional energy dependence of approximately E−1.

Complex formation in the C+(2P)+CH4 reaction at 0.1 to 10 eV

Product distributions are reported for the C+(2P)+CH4 reaction between 0.1 and 10 eV. Upper limits to the fraction of the total reaction involving an excited ethylene ion intermediate are estimated by comparison of product distributions with breakdown curves for ethylene ions. The results indicate a decrease in complex formation at higher translational energies and suggest more direct mechanisms contribute to C2H2u2009+ and C2H3u2009+ formation at higher energies.