Abstract
The interaction of an electron beam of variable energy (2–180 eV) with a beam of neutral carbon dioxide clusters was studied using high resolution mass spectrometry. The ions (CO 2) x +, (CO 2) x CO +, (CO 2) x O +, (CO 2) x C +, (CO 2) x O 2 +, (CO 2) x O − and (CO 2) x O − were observed with x up to 10 and 15 for the negative and positive ions, respectively. The occurrence of (CO 2) x O 2 + is especially exciting, because O 2 + cannot be produced by direct electron ionization of CO 2 and thus this cluster ion has to be created via an internal cluster ion/molecule reaction. Moreover, despite the fact that the neutral clusters are generated under the same expansion conditions, the size distribution of the negative duster ions, in particular of (CO 2) x −, is completely different from that of the positive duster ions. The (CO 2) x − distribution shows pronounced structure, reflecting the intrinsic stability of the CO 2 − solvated by the remaining ligands. In addition, measurements of the stagnation pressure dependence of observed positive and negative ion intensities yields information about the neutral precursor of a specific cluster ion. Furthermore, the electron energy dependences of the negative cluster ions have been measured between threshold and 25 eV, showing a significant difference between the two negative duster ion series observed.
Published Version
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