Gas-Phase Syntheses of Three Isomeric C5H2 Radical Anions and Their Elusive Neutrals. A Joint Experimental and Theoretical Study

Three different radical anions of the empirical formula C 5 H 2 have been generated by negative ion chemical ionization mass spectrometry in the gas phase. The isomers C 4 CH 2 •-, C 2 CHC 2 H •-, and HC 5 H •- have been synthesized by unequivocal routes and their connectivities confirmed by deuterium labeling, charge reversal, and neutralization reionization experiments. The results also provide evidence for the existence of neutrals C 4 CH 2, C 2 CHC 2 H, and HC 5 H as stable species; this is the first reported observation of C 2 CHC 2 H. Ab initio calculations confirm these structures to be minima on the anion and neutral potential energy surfaces.