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

Abstract

The shock-tube technique has been used to investigate the H-abstraction reaction H + Si(OCH) → H + Si(OCH)(OCH) behind reflected shock waves. CHI was used as a thermal in situ source for H atoms. The experiments covered a temperature range of 1111-1238 K, and pressures of 1.3-1.4 bar. H atom concentrations were monitored with atomic resonance absorption spectrometry (ARAS). Fits to the temporal H atom concentration profiles based on a developed chemical kinetics reaction mechanism were used for determining bimolecular rate constants. Experimental total H-abstraction rate constants were well represented by the Arrhenius equation k( T) = 10 exp(-25.5 ± 5.6 kJ mol/ RT) cm s. Transition state theory (TST) calculations based on the G4 level of theory show excellent agreement with experimentally obtained rate constants, i.e., the theory values of k( T) deviate by less than 25% from the experimental results. Regarding H abstractions, we have compared the reactivity of C-H bonds in Si(OCH) with the reactivity of C-H bonds in dimethyl ether (CHOCH). Present experimental and theoretical results indicate that at high temperatures, i.e., T > 500 K, CHOCH is a good reactivity analog to Si(OCH), i.e., k( T) ∼ 1.5 × k( T). On the basis of these results, we discuss the possibility of drawing reactivity analogies between oxygenated silanes and oxygenated hydrocarbons.

Theoretical, Experimental, and Modeling Study of the Reaction of Hydrogen Atoms with 1- and 2-Pentene

“…Ḣ-atom concentrations were monitored behind reflected shock waves by applying the sensitive hydrogen atomic resonance absorption spectrometry (Ḣ-ARAS) technique. The shock-tube apparatus currently used and the method for gas mixture preparation were described previously. , Dilute gas mixtures containing small amounts of ethyl iodide (C 2 H 5 I) as the Ḣ-atom precursor and excess 1-pentene and 2-pentene were prepared, using argon as the diluent.…”

“…The shock-tube apparatus currently used and the method for gas mixture preparation were described previously. 48,49 Dilute gas mixtures containing small amounts of ethyl iodide (C 2 H 5 I) as the H ̇-atom precursor and excess 1-pentene and 2-pentene were prepared, using argon as the diluent.…”

Theoretical Investigation on H-Abstraction Reactions of Silanes with H and CH3 Attacking: A Comparative Study with Alkane Counterparts

“…Peukert et al measured the rate constant for H-abstraction from TeMS and neo -pentane (NPT, C­(CH 3 ) 4 ) with H attacking in a shock tube combined with time-resolved H-atom resonance absorption spectrometry (H-ARAS) and found that their rate constants are similar. They also compared the H-abstraction reaction between tetramethoxysilane (TMOS, Si­(OCH 3 ) 4 ) and dimethyl ether (DME, CH 3 OCH 3 ) and also found that TMOS has similar rate constants to DME over 1111–1238 K at 1.3–1.4 bar . Nurkowski et al .…”

“…They also compared the H-abstraction reaction between tetramethoxysilane (TMOS, Si(OCH 3 ) 4 ) and dimethyl ether (DME, CH 3 OCH 3 ) and also found that TMOS has similar rate constants to DME over 1111−1238 K at 1.3−1.4 bar. 31 Nurkowski et al 32 calculated the rate constants for pressuredependent reactions (OH) 3 SiOC 2 H 5 = (OH) 3 SiOCH 2 + CH 3 and C 2 H 5 OH = CH 2 OH + CH 3 using variable reaction coordinate variational transition-state theory (VRC-TST), which showed comparable rate constants between the two reactions. They also calculated the ethylene elimination reaction of TEOS and found that the rate constant is similar to that of the H 2 O elimination reaction of ethanol.…”