RELATIVE ELECTRON-AFFINITY OF C-60 AND C-70 AND THE STOKES-LAW RADIUS OF THE C-70 RADICAL-ANION IN N-HEXANE BY TIME-OF-FLIGHT MOBILITY MEASUREMENTS

The mobility of the C-70 radical anion in n-hexane at room temperature has been measured by the condensed-phase thin-sheet time-of-flight (TOF) technique. The observed value of 5.2 x 10(-4) cm(2)/(V s) corresponds to a Stokes radius of 5.4 Angstrom, consistent with the molecular geometry of the C-70 molecule as determined by electron diffraction. TOF measurements of anionic mobility in n-hexane, where both C-70 and C-60 are present and compete for photoelectrons, show that the predominant anion changes from C-70(-) to C-60(-) as the C-60 to C-70 concentration ratio is increased from 2 to 20. Quantitative analysis of these ''competition experiments'' shows that the electron affinity of C-70 exceeds that of C-60 by 0.025 +/- 0.007 eV in n-hexane and (through a thermodynamic cycle) by 0.073 +/- 0.019 eV in the gas phase.