We have measured the kinetic energy released in the unimolecular dissociation of fullerene ions, Cn+ --> C(n-2)+ + C2, for sizes 42 < or = n < or = 90. A three-sector-field mass spectrometer equipped with two electric sectors has been used in order to ensure that contributions from isotopomers of different masses do not distort the experimental kinetic energy release distributions. We apply the concept of microcanonical temperature to derive from these data the dissociation energies of fullerene cations. They are converted to dissociation energies of neutral fullerenes with help of published adiabatic ionization energies. The results are compared with literature values.

We report absolute partial cross sections for the formation of selected positive and negative ions resulting from electron interactions with uracil. Absolute calibration of the measured partial cross sections for the formation of the three most intense positive ions, the parent C 4 H 4 N 2 O + 2 ion and the C 3 H 3 NO + and OCN + fragment ions, was achieved by normalization of the total single uracil ionization cross section (obtained as the sum of all measured partial single ionization cross sections) to a calculated cross section based on the semi-classical Deutsch-Märk formalism at 100 eV. Subsequently, we used the OCN + cross section in conjunction with the known sensitivity ratio for positive and negative ion detection in our apparatus (obtained from the well-known cross sections for SF + 4 and SF − 4 formation from SF 6 ) to determine the dissociative attachment cross section for OCN − formation from uracil. This cross section was found to be roughly an order of magnitude smaller, about 5 × 10 −22 m 2 at 6.5 eV, compared to our previously reported preliminary value. We attribute this discrepancy to the difficult determination of the uracil target density in the earlier work. Using a reliably calculated cross section for normalization purposes avoids this complication.

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We have measured the kinetic energy release distributions for unimolecular C 2 loss from singly and multiply charged Sc 3 N@C 78 z+ (z ) 1, 2) and Sc 3 N@C 80 z+ (z ) 1, 2, 3). Using finite heat bath theory, we deduce the dissociation energies of these endohedral ions toward loss of C 2 . The data show that the complexation energies (i.e., the adiabatic binding energies between Sc 3 N and the fullerene cage C n z+ ) are, for a given charge state and within the experimental uncertainty, identical for n ) 76, 78, and 80.