Exotic negative molecules in AMS

“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 [Nucl. Instr. and Meth. B 123 (1997) 532]. M&K were the first to utilize Accelerator Mass Spectrometry to prove the existence of these clusters and a number of other exotic molecules. We review M&K’s efforts and show how their work is being continued at other laboratories. The latest developments are: (1) the discovery of long-lived molecular hydrogen anions H2-,D2- and (2) the unambiguous identification of the smallest doubly-charged negative molecule (LiF3)2−. In particular we show new experimental data for D3-, and for (LiF3)2−, and we try to answer the question why M&K’s search for this di-anion was unsuccessful.