Abstract
Anion photoelectron spectroscopy is performed on the C5 H- species. Analogous to C3 H- and C3 D-, photodetachment transitions are observed from multiple, energetically close-lying isomers of the anion. A linear and a cyclic structure are found to have electron binding energies of 2.421±0.019 eV and 2.857±0.028 eV, respectively. A cyclic excited state is also found to be 1.136 eV above the linear Π2 C5 H ground state. Based on our assignments of the observed transitions and previous calculations on the energetics of neutral C5 H isomers, the cyclic A11 anion state is found to lie 0.163 eV below the A3 linear anion.