Characterization of cyclic and linear C₃H^- and C ₃H via anion photoelectron spectroscopy

Anion photoelectron spectroscopy of C3 H- and C3 D- is performed using both field-free time-of-flight and slow electron velocity-map imaging. We observe and assign transitions originating from linear/bent (l- C3 H) and cyclic (c- C3 H) anionic isomers to the corresponding neutral ground states and low-lying excited states. Transitions within the cyclic and linear manifolds are distinguished by their photoelectron angular distributions and their intensity dependence on the neutral precursor. Using calculated values for the energetics of the neutral isomers [Ochsenfeld, J. Chem. Phys. 106, 4141 (1997)], which predict c- C3 H to lie 74 meV lower than l- C3 H, the experimental results establish c- C3 H- as the anionic ground state and place it 229 meV below l- C3 H-. Electron affinities of 1.999±0.003 and 1.997±0.005 eV are determined for C3 H and C3 D from the X̃ B22 X̃ A11 photodetachment transition of c- C3 H. Term energies for several low-lying states of c- C3 H and l- C3 H are also determined. Franck-Condon simulations are used to make vibrational assignments for the bands involving c- C3 H. Simulations of the l- C3 H bands were more complicated owing to large amplitude bending motion and, in the case of the neutral à Π2 state, strong Renner-Teller coupling.