The decomposition kinetics of chemically activated methyl‐d₁‐methylsilane‐d₂ and ethylsilane‐d₃

Abstract

The decomposition kinetics of chemically activated methyl-dl -methylsilane-dz (DMS-dj) and ethylsilane-d3 (ES-d;) from the Si-D and C-H insertion reactions of CH2 ('AJ with methylsilane-d3 have been studied. The total rate constants for decomposition of chemically activated DMS-dz and ES-d3 have been measured. The individual rate constants for molecular elimination of CHsD, CHzDz, and Dz from DMS-d; and for molecular elimination of CH3CHzD and Dz from ES-dl have been measured. All of the above rate constants exhibit the expected kinetic isotope effect when compared to those found previously in the undeuterated system. RRKM theory calculations of the rate constants for the expected C-Si and Si-D bond rupture processes, based on energetics and activated complex models deduced previously for the undeuterated system, were carried out. In the case of DMS-d; the RRKM theory calculations of rate constants for the bond rupture processes combined with experimental rate constants for the molecular elimination processes gave a total rate constant for decomposition in agreement with the measured value. The results of a high-pressure study of the CH3DKHzDz ratio from chemically activated DMS-d3 decomposition were consistent with complete randomization of internal energy up to a pressure of 4 atmospheres (lifetime of -1.7 X lo-" sec). This is not an unexpected result in light of earlier work.

The Reaction of Hydrogen Atoms with Silyl Radicals; the Decomposition Pathways of Chemically Activated Silanes

“…However, the agreement between theory and experiment with respect to the stabilization of the dimethylsilane molecule indicates that our calculations are quantitatively not too far off. Simons and coworkers [30,8] investigated the decomposition of methylsilanes activated by CH 2 insertion into the Si-H bond e.g. CH 2 + CH 3 SiH 3 -> (CH 3 ) 2 SiH 2 (v) (28) and gave rate constants for the different product channels.…”

“…Energetically much lower fragmentation pathways -silylene formation with concomitant loss of H 2 or CH 4 -are available and are not only realized in thermally activated systems [5,6,7] but also in chemically activated methylsilanes, produced by methylene insertion into the Si-H bond [8].…”

Infrared photochemistry of alkyl- and arylsilanes

“…Product analysis of photolyzed samples (5)(6)(7)(8)(9)(10) torr) of phenylsilane at the 10P(32) line shows the principal product species to be ethylene and acetylene (each ~15% of the total gaseous products), monosilane (~5%), and ethylsilane (1-2%). There were also several other major uncharacterized products and numerous minor products; complete characterization of all the products species was not possible.…”