Anion photoelectron spectroscopy is performed on the C5H- species. Analogous to C3H- and C3D-, 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 2Π C5H ground state. Based on our assignments of the observed transitions and previous calculations on the energetics of neutral C5H isomers, the cyclic 1A1 anion state is found to lie 0.163 eV below the 3A linear anion. [ABSTRACT FROM AUTHOR]