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

The reaction of trimethylsilyl radicals with nitric oxide, Si(CH₃)₃ + NO ↔ Si(CH₃)₃NO, has been studied using pulsed excimer-laser photolysis coupled with time-resolved photoionization mass spectrometry over the temperature range 300-812 K. The standard enthalpy of the reaction was obtained from the measured equilibrium constants using both second- and third-law methods. 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(CH₃)₃NO molecule. The calculated thermodynamic functions of the molecule were used to obtain the standard entropy of the reaction that was used in the third-law thermochemical calculations. The theoretical standard enthalpy of the reaction is in excellent agreement with that determined experimentally using the third-law procedure. The intrinsic Si(CH₃)₃-NO bond strength 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.