Beams of doubly ionized molecules from a tandem accelerator

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Abstract
We report the observation of 3–4 MeV beams of several species of small doubly charged molecules (10B11B++, 10B++2, 11B12C++, 9Be14N++, 12C13C++, 12C13CH++, 12C14N++, 12C2H++, 12CH++2, 9Be16O++, 10B16O++) emerging from a tandem accelerator. These observations significantly increase the number of such molecules known. All are probably produced in metastable states with lifetimes longer than 1 μs. Substantial fluxes (>108 molecules per second was shown for CN++) of these doubly charged molecules were obtained and they were identified by observing the fragmentation of molecular ions after passing through a carbon foil. In some cases the molecules are observed to decay in flight. An efficiency of 10−4 in producing mass 25 molecules (12C13C++ +12C2H++) has been measured. Advantage is taken of the existence of ‘‘atomic interference free’’ mass regions, where no atomic negative ions are formed, therefore allowing the production of pure molecular beams. Some implications of this work for accelerator mass spectrometry (AMS) are discussed. An application of doubly positive charged molecules in a search for doubly negative charged molecules was made, establishing an upper limit of 1:1010 of 10B11B−−/10B11B− and of 1:109 of 12C13C−−/12C13C−.

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