KINETICS AND THERMOCHEMISTRY OF THE REACTION SI(CH3)(3)-REVERSIBLE-ARROW-SI(CH3)(3)H+BR - DETERMINATION OF THE (CH3)(3)SI-H BOND-ENERGY(HBR)

The reaction Si(CH3)(3) + HBr --> Si(CH3)(3)H + Br (1) has been invest igated using flash photolysis/ photoionization mass spectrometry detec tion of Si(CH3)(3) and flash photolysis/resonance fluorescence spectro scopy detection of Br. The measured rate constants are k(1) = (1.06 +/ - 0.13) x 10(-11) exp((6.14 +/- 0.31) kJ mol(-1)/RT) cm(3) molecule(-1 ) s(-1) for T = 296-702 K and k(1) = (8.1 +/- 2.0) x 10(-12) exp((5.12 +/- 0.72) kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) for T = 289-515 K, respectively. The 1 sigma uncertainties represent precision only. Comb ination with k(-1) data and analysis by second and third law methods y ields Delta H-298(o). = -31 1 kJ mol(-1) for (1), with accuracy limits of about +/-2.0 kJ mol(-1). The results imply an Si-H bond dissociati on enthalpy of 397.4 +/- 2 kT mol(-1) and an enthalpy of formation for trimethylsilyl of 16.4 +/- 6.0 kT mol-1.