“…Second, a fluorine has a much larger electron affinity than a hydrogen. Thanks to a better overlap of the wave functions, the 2D surface state continuum, when energetically allowed, is a dominating decay channel for an ion state lying within the band gap [23,28,46]. Moreover, when the binding energy of a negative ion is close to that of the surface state, a coupling of the ion level with the 2D surface state continuum is more efficient than its coupling with the 3D continuum of the free-electron metal states (see a discussion in [46]).…”