Threshold photoelectron-photoion coincidence spectroscopy (TPEPICO) has been used to study the dissociation kinetics and thermochemistry of Me 4Si, Me 6Si 2, and Me 3SiX, (X = Br, I) molecules. Accurate 0 K dissociative photoionization onsets for these species have been measured from the breakdown diagram and the ion timeof-flight distribution, both of them analyzed and simulated in terms of the statistical RRKM theory and DFT calculations. The average enthalpy of formation of trimethylsilyl ion, Δ FH 298K°(Me 3Si +) = 617.3 ± 2.3 kJ/ mol, has been determined from the measured onsets for methyl loss (10.243 ± 0.010 eV) from Me 4Si, and Br and I loss from Me 3SiBr (10.624 ± 0. 010 eV) and Me 3SiI (9.773 ± 0.015 eV), respectively. The methyl loss onsets for the trimethyl halo silanes lead to Δ FH 298K°(Me 2SiBr +) = 590.3 ± 4.4 kJ/mol and Δ FH 298K°(Me 5Si 2+) = 487.6 ± 6.2 kJ/mol. The dissociative photoionization of Me 3SiSiMe 3 proceeds by a very slow Si-Si bond breaking step, whose rate constants were measured as a function of the ion internal energy. Extrapolation of this rate constant to the dissociation limit leads to the 0 K dissociation onset (9.670 ± 0.030 eV). This onset, along with the previously determined trimethylsilyl ion energy, leads to an enthalpy of formation of the trimethylsilyl radical, Δ FH 298K°(Me 3Si .) = 14.0 ± 6.6 kJ/mol. In combination with other experimental values, we propose a more accurate average value for Δ FH 298K°(MesSi .) of 14.8 ± 2.0 kJ/mol. Finally, the bond dissociation enthalpies (Δ FH 298K°) Si-H, Si-C, Si-X (X=Cl, Br, I) and Si-Si are derived and discussed in this study. © 2006 American Chemical Society.