Abstract.A first detection and analysis of negatively charged fragments produced in collisions of fast (20-150 keV) positive hydrogen ions (H +, H + and H +) with gas-phase molecules is presented. The fragments and their abundances were determined by means of a time-offlight mass spectrometer. Negative ions did emerge from every investigated target molecule species, such as halomethanes, sulfur hexafluoride, propane and propene, but in all cases with distinctly lower probability (cross sections in the range 10 -2o-10 -18 cm 2) than positively charged fragments (approximately on the scale 10 -3 or even less). Another essential result is that stable collisionally induced negative fragments are mostly monatomic ions, whereas positive fragments are in their majority more complex polyatomic ions. Furthermore, we observed a direct electron capture from a positively charged but not totally stripped projectile (here: H~-and H +) into stable or very longlived states of the molecular ions SF 6 and 02-, the latter with the largest cross section 18 z 17 2 (t0--10-cm ) found up to now.

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Abstract.Cross sections for the production of O2-in charge transfer collisions of fast molecular hydrogen ions (Hf, Dr, Hf, and Df of 10 to 140 keV kinetic energy) with 02 molecules have been determined by means of a time-of-flight mass spectrometer analysing the slow negative product ions from the collisions. Within the measuring accuracy equivelocity Hf and Df ions have the same cross sections for the generation of Of. The projectile velocity dependence curve of the cross section passes through a broad maximum with a peak value of about 6.5 x 10 -is cm 2 around the Bohr velocity (25 keV/u) before showing an asymptotic decrease still within the limited energy range under investigation that is in inverse proportion to the square of velocity. Throughout the examined energy range H + ions yield a cross section which is about 1.4 times larger than that of Hf ions of the same velocity. The fragment ion O-has been found to appear with cross sections between 10 -19 and 10 -28 cm 2 upon collisional excitation in the energy range under investigation, with ever decreasing intensity when the energy of the positive hydrogen ions, the proton included, was increased.