Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been performed on SeF6 and TeF6 and breakdown diagrams constructed. The ground electronic states of XF6+ (X = Se, Te) are repulsive in the Franck-Condon region, meaning that the first ion signal only gives an upper limit to the energy of the first dissociative ionisation pathway (XF5+ + F + e(-)). Using TPEPICO time-of-flight spectra to determine the kinetic energy (KE) released in fragmentation over a range of energies, however, we have extrapolated to zero KE to calculate values of 14.1 +/- 0.5 and 14.5 +/- 0.6 eV for the first dissociative ionisation energy for SeF6 and TeF6, respectively. Upper limits for the enthalpies of formation of SeF4+, SeF3+, TeF4+ and TeF3+ at 0 K are determined to be 426 +/- 36, 368 +/- 28, 428 +/- 36 and 380 +/- 28 kJ mol(-1), respectively. (C) 2000 Published by Elsevier Science B.V. All rights reserved.