Generation of two isomers of C5H from the corresponding anions. A theoretically motivated mass spectrometric study

Molecular orbital calculations have predicted the stability of a range of c onnectivities for the radical C5H potential surface. The most energetically favorable of these include the linear C4CH geometry and two ring-chain str uctures HC2C3 and C2C3H The corresponding anions are also shown to be theor etically stable, and furthermore, a fourth isomer, C2CHC2, is predicted to be the most stable anion connectivity. These results have motivated experim ental efforts. Methodologies for the generation of the non-ring-containing isomeric anions C4CH and C2CHC2 have been developed utilizing negative ion mass spectrometry. The absolute connectivities of the anions have been esta blished using deuterium labeling, charge reversal, and neutralization reion ization techniques. The success of the latter experiment confirms theoretic al predictions of stability of the corresponding neutral species. This is t he first reported observation of the neutral C2CHC2 species that calculatio ns predict to be substantially less stable than the C4CH connectivity but s till bound relative to isomerization processes.