The dissociative photoionization of tetramethyltin (Me4Sn) and hexamethylditin (Me6Sn2) has been investigated by threshold photoelectron-photoion coincidence (TPEPICO). Ions are energy-selected, and their 0 K dissociation onsets are measured by monitoring the mass spectra as a function of ion internal energy. Me4Sn + dissociates rapidly by methyl loss, with a 0 K onset of E 0 = 9.382 ± 0.020 eV. The hexamethylditin ion dissociates slowly on the time scale of the experiment (i.e., during the 40 μs flight time to the detector) so that dissociation rate constants are measured as a function of the ion energy. RRKM and the simplified statistical adiabatic channel model (SSACM) are used to extrapolate the measured rate constants for methyl and Me3Sn• loss to their 0 K dissociation onsets, which were found to be 8.986 ± 0.050 and 9.153 ± 0.075 eV, respectively. Updated values for the heats of formation of the neutral Me 4Sn and Me6Sn2 are used to derive the following 298.15 K gas-phase standard heats of formation, in kJ•moC-1: ΔfHmo(Me3Sn+,g) = 746.3 ± 2.9; ΔfHmo(Me 5Sn2+,g) = 705.1 ± 7.5; ΔfHom(Me3Sn•,g) = 116.6 ± 9.7; ΔfHom(Me2Sn,g) = 123.0 ± 16.5; ΔfHom(MeSn +,g) = 877.8 ± 16.4. These energetic values also lead to the following 298.15 K bond dissociation enthalpies, in kJ•moC-1: BDE(Me3Sn-Me) = 284.1 ± 9.9; BDE(Me3Sn-SnMe 3) = 252.6 ± 14.8. © 2011 American Chemical Society.