Fragmentation of the valence electronic states of SeF6+ and TeF6+ studied by threshold photoelectron–photoion coincidence spectroscopy

Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been performed on SeF\(_6\) and TeF\(_6\) and breakdown diagrams constructed. The ground electronic states of XF\(_6^+\) (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 (XF\(_5^+\) + 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 \(\pm\) 0.5 and 14.5 \(\pm\) 0.6 eV for the first dissociative ionisation energy for SeF6 and TeF6, respectively. Upper limits for the enthalpies of formation of SeF\(_4^+\), SeF\(_3^+\), TeF\(_4^+\) and TeF\(_3^+\) at 0K are determined to be 426 \(\pm\) 36, 368 \(\pm\) 28, 428 \(\pm\) 36 and 380 \(\pm\) 28 kJ mol\(^{-1}\), respectively.