Kinetics and thermochemistry of Si(CH3)3 + NO reaction: direct determination of a Si-N bond energy

Abstract

The reaction of trimethylsilyl radicals with nitric oxide, Si(CH3)3 + NO Si(CH&NO, has been studied using pulsed excimer-laser photolysis coupled with time-resolved photoionization mass spectrometry over the temperature range 300-812 K. The reaction rate constant was measured as a function of temperature and density (He) in the range 0.82 x loi6 5 [He] I 15.7 x 10l6 molecules ~m -~. Equilibrium constants for the reaction were measured between 685 and 787 K. The standard enthalpy of the reaction Si(CH3)3 + NO Si(CH3)3NO was obtained from the measured equilibrium constants using both second-and third-law methods. The two procedures yielded results in good agreement: m 2 9 8 = -183 f 11 kJ mol-' (second law) and AH0298 = -190.2 f 3.6 kJ mol-' (third law), the latter being more accurate. The high-pressurelimit rate constant of reaction Si(CH3)3 + NO -Si(CH3)3NO, obtained by a short extrapolation of the experimental data using the Troe factorization technique, has a small negative temperature dependence: k,,,, = (3.8 f 0.4) x 10-''(T/298)-(0.6*02). Ab initio calculations with empirical bond additivity corrections have been performed to determine the structure, vibrational frequencies, and energies of the low-lying electronic singlet and triplet states of the Si(CH&NO molecule. The calculated thermodynamic functions of the molecule were used to obtain the standard entropy of the reaction @SO298 = -147.9 J mol-' K-I) that was used in the third-law thermochemical calculations. The theoretical standard enthalpy of the reaction, W 2 9 8 (~a l~) = -190.9 kJ mol-', is in excellent agreement with that determined experimentally using the third-law procedure.The intrinsic Si(CH&-NO bond strength of 187.4 f 4.0 kJ mol-' ( -M o o for the reaction) was determined using the measured enthalpy of the reaction at 298 K (by the third-law method) and the calculated relative enthalpy functions. This study provides the first direct experimental determination of a Si-N bond strength.

Phenyl radical + propene: a prototypical reaction surface for aromatic-catalyzed 1,2-hydrogen-migration and subsequent resonance-stabilized radical formation

“…Switching the reactor material from stainless steel to quartz was also intended to reduce wall reactions that were most clearly manifested by fast hydrogenation of C 6 H 5 to C 6 H 6 . However, even after treating the quartz reactor with boric acid following the procedure of Krasnoperov et al, 22 this manifestation of wall reactions was never entirely eliminated ( Fig. S9, S18, S29 and S33, ESI †).…”

Kinetics and Thermochemistry of the Reaction Si(CH3)3 + HBR ⇌ Si(CH3)3H + Br: Determination of the (CH3)3Si-H Bond Energy

“…To reduce the wall loss rate constant a boron oxide, B2O3, coating was used. 13 Most of the measurements in this study were performed with a 1.05-cm-i.d. Pyrex reactor coated with boron oxide.…”

Effect of Methyl Group Substitution on the Kinetics of Vinyl Radical + O2 Reaction

“…= 1.7 cm) with halocarbon wax coating was used up to 363 K. At higher temperatures a quartz reactor (i.d. = 1.7 cm) with boric acid coating or a Pyrex reactor (i.d. = 1.7 cm) with polydimethylsiloxane (PDMS) coating was employed .…”