Slow photoelectron velocity-map imaging of the CnH− (n = 5–9) anions

Abstract

High-resolution photoelectron spectra of the C_nH⁻ anions with n = 5–9 are acquired with slow electron velocity-map imaging (SEVI). Spectral features are assigned with the help of electronic structure calculations and Franck–Condon simulations. Well-resolved transitions to the linear ²Π and ã⁴Σ⁻ neutral states are observed for species with an odd number of carbon atoms. For C₆H⁻ and C₈H⁻, transitions to the ²Π neutral ground state and the low lying òΣ⁺ excited state are observed. Precise electron affinities, term energies, fine structure splittings, and gas-phase vibrational frequencies are determined. The C₅H⁻, C₇H⁻ and C₉H⁻ SEVI spectra are consistent with the anions having ³Σ⁻ linear triplet ground states.