Beams of fully stripped nitrogen ions have been used to investigate the behavior of the double-to-single ionization cross-section ratio of helium in the 10-30-MeV/amu velocity region. The measured ratio was found to remain nearly constant over this velocity range at a value of 0.01, which is about 4.5 times higher than the high-velocity limit established previously for q = 1 projectiles.

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Data on the production and dissociation of CO~+ molecular ions (where Q = 1 through 7) obtained by ion-ion coincidence time-of-flight measurements were analyzed to determine production yields, dissociation fractions, and branching ratios. A detailed comparison of the dissociation fractions for CO+ and CO + for several collision systems in the same perturbative regime revealed them to be quite similar, whereas the dissociation fraction for CO+ produced by valence-electron photoionization is a factor of 1.8 to 3.6 larger. The results for Q 2 indicated a preference for dissociation channels leading to symmetric or nearly symmetric charge division. An enhancement of the total ionization yields for Q & 4 was observed, and it suggests that electron transfer followed by LMM Auger decay plays an important role in determining the final charges of the dissociation products.PACS number(s): 34.50.s, 35.80.+s, 34.90.+q

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