KINETIC ENERGIES OF TER-THAN-OR-EQUAL-TO-N-GREATER-THAN-OR-EQUAL-TO-4) PRODUCED BY ELECTRON-IMPACT ON C-60() FRAGMENT IONS (58)

We used mass spectrometric techniques in conjunction with the ion defl ection method to determine the kinetic energies of C-n(+) fragment ion s (58 greater than or equal to n greater than or equal to 4) produced by controlled electron impact on C-60 under single collision condition s. The recorded ion beam profiles for the various fragment ions were a nalyzed using two independent methods. One method extracts the average kinetic energy of the fragment ion under study from the measured half -width of the ion beam profile (half-width method), whereas the second method analyzes the entire measured beam profile (profile method). Fo r each C-n(+) fragment ion, the kinetic energies obtained were interpr eted assuming two possible formation pathways, (i) the fission of the excited parent C-60(+) ion in a single-step, two-fragment break-up, C- 60(+)-->C-n(+) + C60-n and (ii) the sequential decay of excited C-60() into C-n(+) via the successive removal of C-m units (m = 1, 2, or 3) . Both the half-width method and the profile method yield very similar results for the kinetic energies of the C-n(+) fragment ions for both formation mechanisms, viz., an average kinetic energy of roughly 0.45 eV in the case of the single-step fission and a linearly increasing a verage kinetic energy from 0.43 eV for the formation of C-58(+) to rou ghly 12 eV for the formation of C-4(+) in case of the sequential decay mechanism (in this case an essentially constant energy of also about 0.45 eV was obtained for the last fragmentation step in each case, whi ch was confirmed by a third method using a fitting procedure). These r esults will be discussed in the context of the most likely fragmentati on mechanism leading to the formation of the various fragment ions. (C ) 1998 American Institute of Physics. [S0021-9606(98)00403-6].