Formation of dianions in helium nanodroplets

The formation of dianions in helium nanodroplets is reported for the first time. The fullerene cluster dianions (C[subscript 60])[subscript n][superscript 2−] and (C[subscript 70])[subscript n][superscript 2−] were observed by mass spectrometry for n≥5 when helium droplets containing the appropriate fullerene were subjected to electron impact at approximately 22 eV. A new mechanism for dianion formation is described, which involves a two-electron transfer from the metastable He[superscript −] ion. As well as the prospect of studying other dianions at low temperature using helium nanodroplets, this work opens up the possibility of a wider investigation of the chemistry of He[superscript −], a new electron-donating reagent.