The electronic structure of HfF5- WF5- and the related species HfFn and WFn is studied using ab initio methods. Computation reveals that the hafnium fluorides are much more stable than the corresponding tungsten fluorides. The detachment energy of HfF5- is 8.8 eV, whereas the corresponding quantity of WF5- is only 3.9 eV. These results show that WF5- can be photodetached while HfF5- is unaffected, and so it is possible by using photodetachment to suppress the interfering isobar (182)Win the ion beam of Hf-182. Such information is the precondition for the successful implementation of a future photodetachment process in Accelerator Mass Spectrometry. (C) 2011 Elsevier B. V. All rights reserved.