For the first time absolute cross sections for electron impact ionization of the hydrogen-like ions B 4+ , C 5+ , N 6+ and O 7+ at electron energies from below threshold up to about 6 keV have been measured using the crossed-beams technique. All measured cross sections are in very good agreement with available distorted-wave exchange calculations and the semiempirical Lotz formula. The behaviour of the classically scaled cross sections along the hydrogen isoelectronic sequence is discussed. A recently developed scaling technique allows us to predict all non-relativistic cross sections along the isoelectronic sequence on an absolute scale.

The electron-impact single ionization of low-charged Ti ions was studied both experimentally and theoretically. Absolute cross sections for Ti q+ ions in charge states q = 1 to 6 except 3 were measured using a crossed-beams technique as well as calculated with the configuration-average distorted-wave method, including both direct ionization and excitationautoionization contributions. For charge states q = 4, 5 and 6, the measurements are in good agreement with the calculations considering that large components of the incident ion beam were in metastable configurations. The cross sections for single ionization of Ti 5+ and Ti 6+ were determined in part with a high-resolution energy-scan method. Besides contributions of excitation-autoionization mechanisms, a remarkable number of structures arising from resonantexcitation double-autoionization (REDA) processes could be observed.

Using the crossed-beams technique the following absolute cross sections σ q,q+n have been measured for the reaction e − + Ti q+ → Ti (q+n)+ + (n + 1)e − : double ionization σ 1,3 σ 2,4 σ 3,5 σ 4,6 σ 5,7 σ 6,8 triple ionization σ 1,4 σ 2,5 σ 3,6 quadruple ionization σ 1,5 σ 2,6 .Measurements for high charge states and ionization degrees, respectively, show significant contributions of inner-shell processes which partly dominate the respective cross section. The results are compared with the scaling laws of Fisher et al and the semiempirical formula published by Shevelko and Tawara, respectively.

Summary. -Absolute cross-sections for electron impact induced fragmentation, fragmentation-single-ionisation and fragmentation-double-ionisation were measured for the fullerene ions C + 60 and C + 58 . For the fullerene ion C 2+ 60 , fragmentation-singleionisation was measured with a loss of n C2 molecules n = 1 ; 2 ; 3. The cross-sections were determined from the respective threshold up to an electron energy of 1 keV using the animated crossed-beams technique.PACS 34.80.Gs -Molecular excitation and ionisation by electron impact. PACS 36.40.Qv -Stability and fragmentation of clusters. PACS 01.30.Cc -Conference proceedings. -IntroductionMany collision experiments with fullerene ions have been carried out in the past few years due to the possibility of the production of intense mass-to-charge-selected fullerene ion beams. Interesting and unexpected results were discovered in these studies. One of the most remarkable features of a singly ionised C + 60 cluster is its exceptional stability against unimolecular decomposition. Nevertheless, the main fragmentation chan-

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