The reaction O(,PJ) + (CH&SiH -products (1) has been investigated by the discharge/fast-flow method with mass spectrometric detection (DF-MS) over 298-773 K and by the flash photolysis/resonance fluorescence (FP-RF) technique over 293-549 K. The rate constants from both methods are in close accord and may be summarized by kl(T) = 5.6 X lo-" exp(-1005 K/7') cm3 molecule-' s-l for 290-770 K. There is reasonable agreement with previous room-temperature studies. kl is larger than k2 for 0 + SiH4 (2), similar to results for triethylsilane and triisopropylsilane [Buchta, Chr.; Stucken, D.-V.; Vollmer, J.-T.; Wagner, H. Gg. Z. Phys.Chem. Neue Folge, to be published], and tri-alkylation is seen to increase the reactivity of the Si-H bonds by similar amounts largely independent of the nature of the alkyl group. This silane activation occurs through lowering the energy barrier to abstraction to form O H + (CH3)3Si*. Ab initio analysis of this pathway at the MP2/6-31G*//HF/3-21G(*) level of theory gives relative energies for the transition states of reactions 1 and 2 that agree well with experiment.
The rates of the reaction of styrene with atomic oxygen have been measured in a discharge flow system with mass spectrometric detection. The measurements were carried out under oxygen atom excess in the temperature range 298 K< T< 873 K. The main reaction channel at room temperature is 0 atom addition to the vinyl side chain, yielding as main product (identified by mass spectrometric product analysis) styrene oxide. Towards higher temperatures 0 atom addition to the aromatic ring as a second reaction channel becomes more important. UsingHammett plots the following Arrhenius expressions for the addition to the aromatic ring (k,) and to the alkene double bond (kdb) of the side chain can be derived: kdp(T) = (0.14*0.03).10'3.~p ( ___ +19r2') cm3mol-l s-l .First experiments with indene give similar results, showing a somewhat higher reactivity for this molecule compared to styrene.
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