Threshold photoelectron-photoion coincidence spectroscopy (TPEPICO) has been used to investigate the gas-phase ionic dissociation energies and thermochemistry of Me 4Ge and Me 3GeX, (Me = methyl; X = Cl, Br) molecules. The 0 K dissociation onsets for these species have been measured from the breakdown diagram and the ion time-of-flight distributions, which were modeled with the statistical RRKM theory and DFT calculations. The measured 0 K dissociative photoionization onsets were as follows: Me 3Ge + + Me (9.826 ± 0.010 eV); Me 3Ge + + Cl (10.796 ± 0.040 eV); Me 3Ge + + Br (10.250 ± 0.011 eV); Me 2GeCl + + Me (10.402 ± 0.010 eV); and Me 2GeBr r + Me (10.333 ± 0.020 eV). These onsets were used to obtain new values for Δ fH, 298o (in kJ/mol) of the neutral molecules Me 3GeCl (-239.8 ±5.7) and Me 3GeBr (-196.5 ± 4.3), and also for the following ionic species: Me 3Ge + (682.3 ± 4.1), Me 2GeCl + (621.1 ± 5.8), and Me 2-GeB r+ (657.8 ± 4.7). © 2006 American Chemical Society.