Reaction Of Hydrogen Atoms with Hexamethyldisilane

Article abstract of DOI:10.1021/j150657a024

The reaction of hydrogen atoms with hexamethyldisilane has been studied by pulsed, mercury-sensitized photolysis experiments using Lyman α resonance absorption and resonance fluorescence detection of H atoms.At room temperature it proceeds exclusively according to H + (CH3)3SiSi(CH3)3 -> (CH3)3SiH (1) with a rate constant k(1) = (3.55 +/- 0.25)E-14 cm³ molecule^-1 s^-1 (T = 295 K).The temperature dependence of the rate constant in molecular units can be expressed by log k(1) = (-10.9 +/- 0.1) - <(1770 +/- 50)/(2.30T)> The pseudo-first-order rate constant for H atom disappearance, K¹, shows a dependence on the initial hydrogen atom to substrate concentration ratio.This is explained by two competing reaction channels for the disappearance of the trimethylsilyl radical: bimolecular combination (k(2)) and combination of hydrogen atoms with trimethylsilyl radicals yielding trimethylsilane (k(3)).From the intensity dependence of k¹ and under the assumption that only reactions 1, 2, and 3 are operative, model calculations yield k(3) = (2 +/- 1)E-10 cm³ molecule^-1 s^-1, while for k(2) only an upper limit of 3 molecule^-1 s^-1 can be given.Thermochemical calculations suggest that the true value for k(2) is lower, probably close to the liquid phase values.