Ionic properties of hydrogenated and fluorinated fullerenes

The ionization potentials (IP) and electron affinities (EA) for a number of hydrogenated and fluorinated derivatives of C₆₀ and C₇₀ have been determined using the charge exchange `bracketing' technique. Samples of C<sub>60</sub>H<sub>x</sub> and C<sub>70</sub>H<sub>y</sub> were prepared by direct solid phase hydrogenation (x = 2-18, y = 2-30) or platinum oxide catalytic hydrogen reduction (x = 36, y = 36). The IP's for C<sub>60</sub>H<sub>2-18</sub> are between 6.75 and 7.53 eV for even x<10 and lower than 6.75 for odd x<10. The EAs for C<sub>60</sub>F<sub>44,46,48</sub> and C<sub>70</sub>F<sub>52,54</sub> were `bracketed' to be 4.0±0.25 eV. The highly fluorinated chiral C_3h molecule C₆₀F₄₈ was observed to directly attach two electrons in the gas phase to produce C₆₀F₄₈^2- and C₆₀F₄₆^2-+F₂. Studies of the metastable decompositions and collision-induced dissociation of C₆₀F₄₈^2- showed fluorine atom and F₂ loss, but no loss of an electron. In addition, the C₆₀F_48,46,44^2- dianions do not charge exchange with molecules possessing high electron affinities, including the neutral parent compound, C₆₀F₄₈ (EA = 4.06 eV). The remarkable stability of C₆₀F₄₈^2- to the removal of an excess electron is attributed to a long-range Coulomb barrier which is built from the bound state for the two electrons near the molecule and the electron-electron Coulomb repulsion between the two at large distance.