High‐Temperature Rate Constants for H + Tetramethylsilane and H + Silane and Implications about Structure–Activity Relationships for Silanes

Abstract

The shock-tube technique has been used to investigate the reactions H + SiH 4 → H 2 + SiH 3 (R1) and H + Si(CH 3 ) 4 → Si(CH 3 ) 3 CH 2 + H 2 (R2) behind reflected shock waves. C 2 H 5 I was used as a thermal in situ source for H atoms. For reaction (R1), the experiments covered a temperature range of 1170-1251 K and for (R2) 1227-1320 K. In both cases, the pressures were near 1.5 bar. In these experiments, H atoms were monitored with atomic resonance absorption spectrometry. Fits to the H-atom temporal concentration profiles applying postulated chemical kinetic reaction mechanisms were used for determining the rate constants k 1 and k 2 . Experimental rate constants were well represented by the Arrhenius equations k 1 (T) = 2.75 × 10 −9 exp(−37.78 kJ mol −1 /RT) cm 3 s −1 and k 2 (T) = 1.17 × 10 −7 exp(−86.82 kJ mol −1 /RT) cm 3 s −1 . Transition state theory (TST) calculations based on CBS-QB3 and G4 levels of theory show good agreement with experimentally obtained rate constants; the experimental values for k 1 and k 2 are ß40% lower and ß50% larger than theoretical predictions, respectively. For the development of a mechanism describing the thermal decomposition of tetramethylsilane (Si(CH 3 ) 4 ; TMS), also TST-based rate constants for reaction CH 3 + Si(CH 3 ) 4 → Si(CH 3 ) 3 CH 2 + CH 4 (R3) were calculated. A comparison between experimental and theoretical rate constants k 2 and k 3 with available rate constants from the literature indicates that Si(CH 3 ) 4 has very

Theoretical study on the kinetics and thermodynamics of H‐atom abstractions from tetramethylsilane‐related species

“…The energy barrier obtained at the G4 level of theory from our work agrees well with their result. Rate constants obtained in these two works agree well with the experimental data in the literature 40 . Arthur et al 42 .…”

“…Arrhenius plot of R1: Si(CH 3 ) 4 + H ⇌ Si(CH 2 )(CH 3 ) 3 + H 2 total rate constants. Blackline: theory (G4), present work; red line: theory (G4), Peukert et al 40 43 …”

“…In this section, all rate‐constant data represent total rate constants. Peukert et al 40 . suggested comparable reactivity toward H‐atom abstractions on methyl sites between TMS and neopentane for the similar dissociation energies (D H 298 ) of the C–H bonds in both compounds.…”

High-Temperature Rate Constants for the Reaction of Hydrogen Atoms with Tetramethoxysilane and Reactivity Analogies between Silanes and Oxygenated Hydrocarbons

“…To rationalize the findings reported in this work, the experimental data were supported by TST calculations. Since the G4 composite approach has been previously used for calculations of energy profiles of chemical processes, ,− TST calculations were based on molecular properties and energetics at the G4 level of theory. The rate constants for H abstractions were calculated using TST, as implemented in the KiSThelP code .…”

“…This was also shown in a recent H-ARAS (atomic resonance absorption spectrometry) shock-tube study from our laboratory, where we have investigated the reactions H + SiH 4 → H 2 + SiH 3 and H + Si(CH 3 ) 4 → H 2 + Si(CH 2 )(CH 3 ) 3 (SiH 4 , monosilane; Si(CH 3 ) 4 , tetramethylsilane). 8 It was found that Si(CH 3 ) 4 and neopentane (C(CH 3 ) 4 ), which is the analogous hydrocarbon to Si(CH 3 ) 4 , have similar reactivity toward H abstractions. On the other hand, SiH 9 This result is interesting in terms of possible reactivity analogies between silicon-organic molecules and corresponding hydrocarbons.…”