Exploring 1,2-Hydrogen Shift in Silicon Nanoparticles: Reaction Kinetics from Quantum Chemical Calculations and Derivation of Transition State Group Additivity Database

Abstract

Accurate rate coefficients for 35 1,2-hydrogen shift reactions for hydrides containing up to 10 silicon atoms have been calculated using G3//B3LYP. The overall reactions exhibit two distinct barriers. Overcoming the first barrier results in the formation of a hydrogen-bridged intermediate species from a substituted silylene and is characterized by a low activation energy. Passing over the second barrier converts this stable intermediate into the double-bonded silene. Values for the single event Arrhenius pre-exponential factor, A, and the activation energy, E(a), were calculated from the G3//B3LYP rate coefficients, and a group additivity scheme was developed to predict A and E(a). The values predicted by group additivity are more accurate than structure/reactivity relationships currently used in the literature, which rely on a representative A value and the Evans-Polanyi correlation to predict E(a). The structural factors that have the most pronounced effect on A and E(a) were considered, and the presence of rings was shown to influence these values strongly.

Identification of higher order silanes during monosilane pyrolysis using gas chromatography-mass spectrometry

“…The signal corresponding to the molecular ion (m/z 32) is rather weak. The even weaker signal at m/z 33 and m/z 34 (not visible) are isotope peaks caused by the natural abundances of 29 Si, 30 Si and 2 H. There is good agreement between our measured mass spectrum and the mass spectrum from the literature [66] (Fig. 4a, lower pane).…”

“…It is commonly accepted that the pyrolysis occurs through a series of chemical reactions, including SiASi bond formation and hydrogen elimination, producing silanes with increasing number of Si atoms [13,20,22,23,28,29]. Additionally, 1,2-hydrogen shifts, ring opening and ring closing lead to interconversion between different isomers within each silane family [22,23,30,31]. Many of the kinetic models of the monosilane pyrolysis process have an impressive degree of detail, some of which include hundreds of species with up to 10 Si atoms and more than one thousand chemical reactions [16,[21][22][23]27].…”

Kinetics of α hydrogen abstractions from thiols, sulfides and thiocarbonyl compounds

“…The method has proven to be successful in predicting rate coefficients of addition reactions and hydrogen abstractions for hydrocarbons 26,34 and H 2 additions, 1,2-hydrogen shifts and cyclization reactions for silicon-containing compounds. [35][36][37] The aim of this work is to extend the previously developed additivity schemes for Arrhenius parameters of hydrogen abstraction reactions between hydrocarbons to sulfur containing compounds. 25,26 To this end, Arrhenius parameters are obtained from high-level quantum chemical calculations.…”

Kinetics of Substituted Silylene Addition and Elimination in Silicon Nanocluster Growth Captured by Group Additivity

“…Each of these reactions exhibits dative bond formation that stabilizes the divalent silicon atom. [80,83] The formation of an adduct from the separated reactants is always exothermic, and no enthalpic barrier was observed for any of the reactions under pyrolysis conditions. The heat of reaction at 298 K and 1 atm for this addition averaged À12 kcal mol…”

“…This approximation was used successfully in hydrocarbon chemistry [56][57][58] and in our work in which substituted silylene-silene isomerization was examined. [80] The primary silicon atoms were differentiated according to the number of Si and H atoms to which they were attached. The seven primary acyclic contributions to the reactive center used in TSGA were: 1) Si 2 -(H) 4 2 , where the subscripts on the Si atoms denote the particular atom in the reactive center ( Figure 3) and the subscripts after parentheses denote multiple attached atoms.…”