"The techniques and equipment developed for AMS studies are well suited for identifying exotic negative ions." With this sentence begins a pioneering paper by Roy Middleton and Jeff Klein (M&K) on small doubly-charged negative carbon clusters [1]. M&K were the first to utilize an AMS system to prove the existence of these and a number of other exotic molecules. For an unambiguous identification M&K concentrated on ions with an uneven mass number, e.g. (12C913C)2–, so the doubly-charged negative molecules are injected at a half-integer mass. Due to the stripping process in the tandem accelerator, the molecules break up into their atomic constituents and the atomic ions are again analyzed by their mass-to-charge ratio and by their energy in the detector. In this contribution we will review M&K's efforts in this field and show how their work continued at other laboratories. The latest developements are: (1) the unambiguous identification of the smallest doubly-charged negative molecule (LiF3)2–, first observed at IsoTrace [2], and then at VERA, and (2) the discovery of long-lived molecular hydrogen anions H2– and D2– at VERA [3]. We believe that these discoveries also show the great versatility of the Middleton-type sputter source - which may well have more surprises in store.
[1] R. Middleton and J. Klein, Nucl. Instr. Meth. B 123, 532 (1997).
[2] X-L. Zhao and A. E. Litherland, Phys. Rev. A 71, 064501 (2005).
[3] R. Golser et al., Phys. Rev. Lett. 94, 223003 (2005)].
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See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)