The dynamics of reaction of Cl atoms with tetramethylsilane

Abstract

Rotational state distributions and state-selected CM-frame angular distributions were measured for HCl (v′ = 0, j′) products from the reaction of Cl-atoms with tetramethylsilane (TMS) under single collision conditions at a collision energy, E_coll, of 8.2 ± 2.0 kcal mol⁻¹. The internal excitation of these products was very low with only 2% of the total energy available partitioned into HCl rotation. A transition state with a quasi-linear C–H–Cl moiety structure was computed and used to explain this finding. A backward peaking differential cross section was also reported together with a product translational energy (T′) distribution with a maximum at T′ ∼ E_coll. This scattering behaviour is accounted for by reactions proceeding through a tight transition state on a highly skewed potential energy surface, which favours collisions at low impact parameters with a strong kinematic constraint on the internal excitation of the products. The large Arrhenius pre-exponential factor previously reported for this reaction is reconciled with the tight differential scattering observed in our study by considering the large size of the TMS molecule.